The grammar is not great, but what you have written is perfectly understandable - however, I would do a test that is more related to your work and "hide" the below average score for English.
It's your work that counts. I love your illustrations!
Lora, Logo Design Studio is not a professional tool for creating logos - basically, it is just a large collection of cheap looking templates and ready-made elements. Upwork is a competitive market - you will not survive here if you are planning to sell recycled templates. If you want to design real logos, you should learn using one of the industry standard vector designing tools: CorelDraw, Adobe Illustrator or maybe (the free) Inkscape.
At the moment you portfolio is not too impressive - upload your very best logo designs and illustrations before start applying for jobs.
re: "I can not find where exactly is the problem whit those grammatical mistakes. I found everything corect. Please help me to start."
It is important for you to understand that you do not possess the ability to accurately judge whether or not your grammar, spelling, language usage, etc. is correct.
Your options are to:
a) decide that you don't care whether or not everything is correct
b) hire sombody else (or find a willing volunteer) to proofread and correct your mistakes
But maybe it does not matter.
When I hire artists, I look at their portfolios. I do not read their overview text. I do not read their cover letters. I do not talk to them and I do not care whether or not they speak English. I provide clear instructions, and I am pleased at their results when they submit artwork. Being able to use English without errors is not a factor for me when hiring visual artists. But to put your best foot forward for clients generally (not just me), it can be a good idea to present error-free text on your profile page, with the help of a native English speaker.
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