Couple a couple days a couple times What it means?

Preposition In or At I found sentences in the form below.  S Verb in adverb (place)  S Verb at adverb (place)  Any one can explain when we use in or at in this form?

When we use the preposition? I found sentences in the form below. 

S Verb in adverb (place) 
S Verb at adverb (place) 

Any one can explain when we use in or at in this form? 

When we use this preposition? I found sentences in the form below. Any one  can explain when we use in or at  in this form? 

"S Verb in the (adverb) place"
"S Verb at the (adverb)  place"

Confusing, which is the correct? What is happening in there? 
OR
What is happening there? 

What the Different Would you guys like to tell me what the different betwen "at the momment" and "right now"? Thanks

Did I wrote correctly? 1."Enjoy the current live,  the future will comes"

2. "I am going back to work"

Guys,  did I wrote correctly? 

Can we say "What happens? " Can we say "What happens? "/ "What does happen?"

Dear all Friend. When we use It's and its exactly?