Find the first 4 terms of the arithmetic sequence.
f(n) = f(n-1) + 5
f(1) = -2

f(n) = f(n-1) + 5   simply means

the next term or f(n), will have a value of
the one before it, or f(n-1), +5

so.. you're looking for the 4th term, that means f(4)
to get 4th term then, that will be the 3rd term plus 5,
whatever the 3rd term is

now... f(1) = -2, simply means, the term 1, or f(1), or first term, is -2

now to find a term value in an arithmetic sequence 

and I'm sure you know what f(1) is, so, just plug it in, to get f(4), or 4th term