when I have to use "like a" or "as a" to compare something? Sorry if the question is wrong :$ For example: "She is like a monkey" or "She is as a monkey" Thank yoooou!

How I can be more confident with my English? When I have to communicate with an English speaker I feel really nervous. This makes me feel insecure and I made some mistakes that I wouldn't have if I talk with "myself" or when I have to write it. I need some techniques or advices to control my feelings and get to have a fluent communication. Thank you!