Good morning!
That might seem a silly question but… How do I know I am casting spells properly?
I am learning every day more and more and this world is fascinating but I don’t want to do it wrong!
I am building my altar slowly and I feel around my altar there is so much peace. I love spending time meditation around it.
Blessed be 
Good morning, @nuria! 
Not a silly question at all- I think it’s a great thing to ask! It is perfectly natural for new witches to feel some spell anxiety while they are starting out. No worries- as you do spells and find your own unique practice, confidence will come to you 
When it comes to if a spell is being cast properly- it all depends on the requirements of each individual spell. To feel more comfortable, you can ask yourself two things:
Did I follow the spell instructions?
If yes- then that’s a great sign! But it also doesn’t mean the spell will go bad if you didn’t follow each step. It is absolutely okay to substitute ingredients or omit things. If you ever feel unsure about a step (or are looking for a good correspondence/substitution)- feel free to give a shout in the forums and get some suggestions! 
How do I feel after the spell is done?
This is perhaps the best indicator of if a spell went well- if you feel satisfied and accomplished at the end of the ritual work, then it very likely means that all is in order 
It may take some time before the beginner’s worries grow into natural confidence- so keep experimenting with different spells and explore what works best for you!
To help build Casting Confidence:
I highly recommend the Guided Meditations- they give step-by-step instructions and some even have a video/audio walking you through the steps. It helps to build confidence! 
There’s also the Spellcasting 101 Course- you may find the “Step-by-step spell casting” section and “Signs your spell is working” section to be helpful.
Good luck and Happy casting! 
@BryWisteria has shared some great resources with you in regard to spellcasting, so definitely check those out.
One of the first things I ever recommend to anyone learning how to cast spells or practice witchcraft is energy work. To put it simply, energy work is the practice of learning to feel, control, and sense energy in everything around us. In my practice, when we cast spells, this is all we are doing. We are using the energy of the objects we use, manipulating the energy we already have, and giving it a new direction. All it takes is one simple change of energy to get results.
Once you get more comfortable with energy work, it will be easier to tell whether your spells are headed in the right direction or if they’re just not going to work. I might write an entire post on energy work, best practices, and exercises – for now, though, I’ll just share some resources
Energy Work – Hellenic Witchcraft
Energy Work – Black Witch Coven
Energy Sensing Exercise – Black Witch Coven
6 Witchcraft & Energy Work Practices to Try – Anya Esma (YouTube)
Thank you for this response! This is a question that has sometimes popped up in my thoughts as well. I feel more confident in knowing that I have followed the spell instructions (with modifications if necessary) and gauging how I feel after casting. Fantastic indicators.
I agree with everything said here. It is about intention, energy work, shadow work, getting comfortable with yourself, and knowing there is no wrong way - as long as you aren’t hurting someone or trying to control them.
The only thing I would add is setting correct expectations. Our spell work is different from what is seen in movies and tv shows. While healing can happen, it needs to be working with science. The moon can reveal itself during a thunderstorm, but it can decide not to, also. Communication across vast distances without the aid of the internet or phones can happen, but you might just need to turn on a computer or pick up the phone. Sharing dreams, waking up at just the right moment, sending that note of encouragement at just the right moment, and seeing blue orbs and white auras, all can happen. (These all happened to me.)
Hope for these things but remember we live in the natural world and it takes supernatural events for us to experience. You are not doing anything wrong if you don’t get these things every time you do spell work. There is nothing wrong with your magic. This stuff happens when the universe says it needs to happen for you.
Edit: This sounds somewhat dogmatic and matter of the fact. I encourage others to correct me, if needed. There is always room for discussion and different realities for different people and I would be happy to be wrong.
I don’t think that sounds dogmatic at all @praecog29 
if we have our expectations set too high and think our magic is going to work like we see on tv, then we’re just going to be disappointed and may even give up altogether 
I’m a huge believer in putting the magical effort (spells, rituals, charms, etc.) while backing that effort with mundane work.
It’s like that example that people always use – you can do a million spells to get a job, but if you never put an application in, how are people supposed to know they can hire you?
I have always used my intentions and paid attention to how I feel during and after the spell. I try to keep my anxiety in check but sometimes just performing the spell, I get so excited and then I get anxious and want to move through it. So I try to focus my intentions and feelings toward the spell and what is going on and then use how I feel after the work is done.