How to improve your English grammar
Don't get too hung up on having perfect grammar, but don't think it doesn't matter either. The main point of learning a language is to be able to communicate, and using the wrong grammar can lead to misunderstandings, so you do need to get the words in the right order. That said, learning about a language is different to learning a language. As a child we learn to communicate without the benefit of grammar books.
Of course you're an adult, and as such you can use grammar books to read about English grammar and to test your grammar, but once you think you've learnt something you have to practise it again and again, and in a more realistic situation than on a blank sheet of paper. Practise forming meaningful sentences. Make positive statements negative, turn statements into questions, make active statements passive. Turn past tense sentences into present tense sentences etc. etc.
Learn the different tenses. Learn by heart a simple example sentence using each tense.
Do online exercises. Keep a note of how you did and go back in a few weeks/months to see how you have improved.