My difficulties

I spoke today with a native in English. It was terrible! I couldn't say to him two words (I couldn't say two words to him)! I told him all times "mmm.." All I said was 'mmm..". It was a shame to for me!
I should raise the lexicon I should/need to improve my vocabulary. But how? All time cram Cram/study all the time? How do you usually raise your lexicon improve your vocabulary? Also I get/become confused in with English tenses. It's so difficult!

A lot of work is necessary to for me!

http://www.memrise.com <- a good website for learning vocabulary

The more you practice with native speakers, the more you'll get the hang (better understanding) of tenses because they can be tricky. Don't be afraid to make mistakes! You already know a lot :)