Three questions (Thanks for answerring)
1- Why is the follow sentence right? "Kommst du mit, wenn du Zeit hast?" I understand it means will you come when you have time? BUT my question is why it isnt "Kommst du mit dich, wenn du Zeit hast"?

2- what is the difference between kennen and wissen?

3- what is the difference between hilfe and helpen?

I would deeply appreciate for your kind answers. :D

Question

Three questions (Thanks for answerring)
1- Why is the follow sentence right? "Kommst du mit, wenn du Zeit hast?" I understand it means will you come when you have time? BUT my question is why it isnt "Kommst du mit dich, wenn du Zeit hast"?

2- what is the difference between kennen and wissen?

3- what is the difference between hilfe and helpen?

I would deeply appreciate for your kind answers.  :D

Answer

Thanks for all your kind answering. I think I am now clear on this language point. Vielen Dank!!!

Answer

Hallo, wie geht's?

1- With the verb mitkommen you don't have to use any pronoun to express with whom the person is coming. It's clear from the context:
Wir gehen ins kino, kommst du mit? (you don't have to add "uns").
Ich gehe in das Schwimmbad, kommst du mit? (you don't have to add "mir").

2- To explain the difference/s in a synthetic way is not easy, both meaning "know". But kennen is normally used when you get to know of the existence of something or somebody. It's a bit like the chinese verb 认识。On the other side, wissen refers, in general, to "having the knowledge of something". Similarly to the meaning of 知道。But this explanation is very simple and there are many exceptions. You will know (wirst wissen) which one to use with practice.

3 -Hilfe is the substantive: Sie braucht Hilfe: 她需要帮助
   -Helfen (not helpen!) is the verb: Bitte, helfen Sie mir / Please, help me / 请帮助我.
Hope it helps you.

Answer

Kommst du mit = come along (with us)
It doesn't mean just "come".

Answer

As in any language, many sentence try to leave out things that are commonly understood.
In this case, the full sentence would be:
"Kommst du mit mir, wenn du Zeit hast?" - is shortened to:
"Kommst du mit, ...."  - the 'mir' is understood.  It is a common form and considered completely correct.

2. Kennen means to be aquainted with, as "Kennen sie miene Schwester" - Do you know my sister? This means more "Are you acquainted with my sister?"
Wissen refers to knowledge.  "Ich weiss nicht wo ich bin."  - I do not know where I am."

3 Helpen is, I believe, Germlish - a word like upgedated (updated) which is borrowed from English.  It is not a 'real' German word.

Answer

ni hao shu!! Kommst du mit, wenn du Zeit hast? Das heißt: Kommst du mit mir, wenn du Zeit hast? Kennen:Ich kenne jemanden. Ich kenne eine Stadt. Ich kenne das Buch, das du gerade ließt. Wissen: Ich weiß, wohin der Weg führt. Ich weiß, dass heute Mittwoch ist. Kennen bezieht sich auf Gegenstände oder Orte. Hilfe (Die Hilfe) ist ein Nomen. Helfen ist ein Verb! Ich brauche unbedingt Hilfe beim Lernen! Ich kann dir helfen, Deutsch zu lernen. Ich hoffe, meine Hilfe hilft dir!! Schönes Wortspiel, - oder?