Hello Snezana,
Snezana wrote:Indeed, what really influences person's future carrer, are one's achievements, or better to say, success in one or another field in school.
As you certainly know, there are infinite ways of putting your thoughts in words. My advice is to always look for the simplest and clearest one. Let me show you some grammar problems in your sentence:
1. what really influences (singular) ... are one's ... (plural) (concordance error)
2. ... future career, are (you never put a comma between the subject and the verb)
I wouldn't write that sencente that way myself, but that's a matter of style. Here you have its correct version:
Indeed, what really influences the future of people's career are their achievements, or better to say, their success in one or another field in school.
Buggah Loo