@kostitras777,
I don't speak Czech either, and unfortunately don't know even a little bit about the grammar, but hopefully this will be somewhat helpful.
1. From looking at the original abstract, Czech doesn't seem to use "the," "a," or "an," which means you don't use "the" where it should be used a lot of times. It's almost never grammatically wrong to add "the" in front of nouns in English.
In Czech, it might be proper to say "boy saw girl," but in English you need to say "a boy saw a girl," or "the boy saw a girl," or "the boy saw the girl." Sorry if that's confusing.
Here are some examples from your abstract.
a) Práce představila způsoby farmakologické a nefarmakologické léčby a její případné komplikace spojené s vyšším věkem.
The thesis presented methods of pharmacological and non-pharmacological treatment and its possible complications associated with older age.
b) V dalších kapitole práce byl popsán ošetřovatelský proces,
The next chapter described the nursing process,
Look out for those extra thes and ans and as if you can!
2. You use "was" as a helping verb to another verb a lot: "was introduced," "was investigated," and "was assessed." There may be more that I didn't catch. In English, it's best to put these after the subject they pertain to.
Examples from your abstract.
a) Diplomová práce byla mířena teoretickým směrem, ve kterém byl představen pojem deprese.
This thesis was focused theoretical direction in which was introduced the concept of depression.
You got the first one correct. "was focused" describes the subject, "this thesis."
"was introduced" is incorrect because it's unclear what it describes, which should be "the concept of depression."
This thesis was focused
on theoretical direction in which the concept of depression
was introduced.
b)Z důvodu zvýšené sebevražednosti zapříčiněné depresivní poruchou byla představena i problematika suicidálního jednání seniorů
By reason of increase suicide rate caused by depressive disorder was introduced the issue of suicidal behavior in the elderly.
By reason of increase
d suicide rate caused by depressive disorder the issue of suicidal behavior in the elderly
was introduced.
3. I don't want to completely rework your abstract, but a lot of the word choices you use in Czech might not be the best in English. I'd try to stay away from past tenses, unless you're talking about the method of the project.
Try to stay in active voice as much as you can.
For example,
a) This thesis was focused theoretical direction in which was introduced the concept of depression.
This thesis
focuses on theoretical direction, which
introduces the concept of depression.
In English, this wording sounds clearer and more direct.
Hopefully some of this helps, and doesn't overwhelm you/isn't too hard to understand.