How can tell "refuse" and "reject" ?

Basically Niki, "refuse" implies an offer or request whereas "reject" is a bit more general, a refusal to consider. Hope we'll hear some more subtle diffs

Tes, help

Thank you so much!

You're welcome, Niki; it's the least I can do

But Tes, I'll bet you can elaborate

When you refuse something, you don't accept it.
" The girl refuses to take her medicine"

When you use reject, you not only don't accept something, you flat out don't want to go any further.
" The promotion was rejected by his supervisor"

Reject can also be as noun -
"The dress was a reject and thus much cheaper"

Refuse something means that you don't accept it.
If you reject some work means that you don't want to do the work.

Selectmytutor needs to stop responding to English language learners' threads, as "she" is obviously not a native speaker of English.