What should I do after I memorize Hiragana and Katakana?
I am learning japanese, and i spent a lot of time trying to learn hiragana and katakana. i suppose kanji comes next.. (but... it is too hard). Do you think i should continue memorising kanji words and phrases or can i actually start learning some grammar? are there any good websites i could use? or any tips?

Question

Answer

I would start learning the language structure and words.  At the same time, pick up some of the more common Kanji along the way.  Kanji is actually easier to understand if you know some of the words and patterns.  So, learn them side-by-side.

Answer

Yeah :) You can learn grammar and new words

Try these sites :) They are really really good
http://japanesetest4you.com/
http://www.guidetojapanese.org/learn/

Answer

of course you can start learning grammar.
I don't remember right now by heart any good web pages for grammar, but there are many, even wiki has some good explanations.

you might want to take a look at this link for example:
https://en.wikibooks.org/wiki/Japanese/Grammar/Verbs