I am a bigginer of russian language.What does "prosta" mean?
I hear many time this word in russian conversation

Question

Answer

The word «ПРОСТО» has several meanings in the Russian language.

1. easy

For example,
Учить русский язык не так-то ПРОСТО. - Learn Russian is not so EASY.
Управлять автомобилем ПРОСТО. - Driving is EASY (not difficult).

2. modestly

For example,
Она одета ПРОСТО. - She dressed MODESTLY, not rich

3. just
For example,

Я не хотел делать это. ПРОСТО у меня не было выбора. - I did not want to do it. I JUST have no choice.

Additionally, the word "ПРОСТО" is a filler word in Russian.

Answer

Просто - simply, just

Answer

I hear many time this word in russian conversation
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In that meaning: "Just". 
E.g.
Не обращай на него внимания, он просто мудак. Do not mind him, he's just an asshole.

Answer

просто = merely