Hi everyone, I tryam trying to learn english writing skillhow to write in English.

If you are writing about an ongoing event(I am trying) you need to use the verb am(to be) and the -ing ending to signal that it is something you are currently doing. Also, I think that "how to write in English" fits the context better than "English writing skills".

Today I ran 5 km in the woods.

The woods are plural and will therefore end in a plural -s

Hi everyone,! I'm trying to learn eEnglish writing skills.

Maybe 'practice' would work here instead of 'learn')

Today I ran 5 km in the woods.

Wood - a material from trees
Woods - лес

There were many people in the woods because today is Saturday.

When I runnedan under the open sky, the sun is strong burniwas burning strong.

The past tense of 'run' is 'ran' :3
Stick to one tense, you began with the past tense and then continued onto the present tense

RFor the remaining 4 km, I ran at athe speed of 1km per 6 min.

Remember articles :3

TheMy maximum heart rate was 183.

You are talking about yourself here, so I would use 'my'

TheMy average heart rate was 170.

It is a very big numbers, so I need to reduce its to an average of 160.

Either - it is a very big NUMBER
or - they are very big NUMBERS
Use infinitive verb - TO reduce

PThis is probably because of this is 5 days ago I donated donormy blood, and my organizme donsms haven't fully recover.ed.

Sentence structure difference and also some tense problems here

I plan next runnto run againg on Monday and I will see what will come of it.

Good sentence but you need the infinitive verb - to run, in this sentence :3

Hi everyone, I try to learnimprove my english writing skills.

Today I ran 5 km in the wood.s.

There were many people in the woods because today is Saturday.

When I runnedan under the open sky, the sun is strong burningwas bright.

RThe remaining 4 km I ran at a speed of 1km per 6 min.

It is a very big numbers so I need reduce its to average 160.

Probably cause of this is 5 days ago I donated donor blood and my organizme dons didn't fully recover.

I am planning my next running on for Monday and I will see what will come of it.