i am confused on making sentence in Japanese
i have learn hiragana & katakana particles and some vocabularies.
For a simple sentence i don't have problem...but when it goes to more complicated sentence requiring change of form like past tense, negative sentence etc it's very hard.
Any suggestion for me how to learn structure in systematic way?
Doumo arigatou

Question

Answer

I think what you need to do is...
memorize simple phrase
read aloud it
Find Japanese friend 
Use and fix it

cuz babies learn to use language by imitating how parents speak, while they never learns grammars. 
Go for it!