let vs. let's

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hi Dear

Can you elaborate the difference between let’s and let.

and secondly which form of verb is used with “ONCE” and how to use “ONCE” in an english language.

2

let’s = let us
let’s go = let us go

it is the contraction in writing

It seems a lot of verbs using with once. I think you should look up the dictionary to understand the usage for “once”.
Ex : love me once again.