I'm new here,: I was searching for a long time a website like this where I could write some short stories, and get feedback to improve my English.

Perhaps, I willI might make many grammartical mistakes because I won't use any help from Google Translate, but I'll thank you so much if yoube grateful if you could help me with corrections. ¶
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I'm a Spanish native speaker, i. If I can help you with anything abouto learning Spanish, tell me.

Perhaps, I will make manyI might make a lot of grammar mistakes because I won't use any help from Google Translate, but I'll thank you so much if youd be happy if you could help me with corrections. ¶
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I think this is the best sentence here.

I'm new here, I was've been searching for a long time for a website like this where I could write some short stories and get feedback to improve my English.

Perhaps, I will make many grammartical mistakes because I won't use any help from Google Translate, but I'll thank you so muchso I'd appreciate if you help me with corrections. ¶
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I'm a Spanish native speaker, so if I can help you with anything abouto learning Spanish, tell me.

I'm new here, I wasand I've been searching for a long time for a website like this where I could write some short stories and get feedback to improve my English.

The other corrections people have given work just as fine.

Perhaps, I willI might make many grammar mistakes because I won't use any help from Google Translate, but I'll thank you so muchbe grateful if you help me with corrections. ¶
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I'm Spanisha native Spanish speaker, so if I can help you with anything abouto learning Spanish, tell melet me know.

"let me know" sounds a bit softer or more friendly

I'm new here,. I washave been searching for a long time for a website like this where I could write some short stories and get feedback to improve my English.

Perhaps, I willI might make many grammar mistakes because I won't use Google Translate (or, I won't get any help from Google Translate), but I'll thank you so muchd be so thankful if you could help me with corrections. ¶
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I'm Spanisha native speaker, i of Spanish. If I can help you with anything in regards to learning Spanish, tell melet me know.

"Tell me" sounds more like a command while "Let me know" sounds more like a kind offer of assistance :)

I'm new here,. I was've been searching for a long time for a website like this where I could write some short stories and get feedback to improve my English.

Perhaps, I willI might make many grammar mistakes because I won't use any help from Google Translate, butso I'll thank you so muchreally appreciate it if you help me with corrections. ¶
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I'm Spanish native speaker, so if I can help you with anything to do with learning Spanish, tell melet me know.

I'm new here,. I was searching for a long time for a website like this where I could write some short stories and get feedback to improve my English.

Search [something] ❌
Search for [something] ✔

Perhaps, I will make many grammar mistakes because I won't use any help from Google Translate, but I'll thank you so muchbe so thankful if you help me with corrections. ¶
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"I'll be so thankful" is more natural sounding, while "I'll thank you so much" sounds unnatural.

I'm a native Spanish native speaker, if I can help you with anything tofor learning Spanish, tell me.

"anything/something for [verb]ing" sounds better here.

"Do you have anything to eat" = "Do you have anything I can eat" ✔
"Do you have anything for eating" = "Do you have anything that one can *use* to eat" ❌ (unnatural, sounds like you're asking for silverware or plates)

"Do you have anything to learn" = "Do you have anything you can learn" ❌ (unnatural, sounds like you're asking for someone to "give" you school subjects or lessons)
"Do you have anything for learning" = "Do you have anything I can use for learning" ✔ (this fits your sentence)