I understand what you're trying to say here. Overall your letter does have structure - you have an opening, a middle and a closing section. Is your friend called Fer? In that case, you should address your letter to Fer.
Dear Fer,I actually really like what you've written and grammatically it's nearly there. With the most minimal of tidy-ups, I put this, being careful to use your words:
We have been studying English for almost 6 weeks now. I think you have learned a lot because you have the will that makes it possible to learn faster. Now we can use all the words you have learned and have a conversation. And remember that when you are writing a letter you should always finish it appropriately. As Fer is your friend, you should use:
Yours sincerely,I hope this has helped in some way. If I can help anymore, please do send a message.
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