Simple Search by field query

I'm using the C# library to query a string in my cluster, but keep getting back results thats outside the string i want to search for. I basically want something on the lines of 'Select * where field = 'some value'

In fluent, how is this accomplished cause my test arent retrieving the desired results. also, how can one use the .keyword ext?

This is what i currently have...
.Query(q => q
.Bool(m => m
.Must(t => t
.Match(f => f.Query(nsID).Field(fie => fie.nS2ID).Operator(Operator.And)) && ,,,,,

I just want to search for documents in the NS2ID field that matches the nsID i pass it.

Any insight would be helpful

Thanks,