S(1) is the first term of the sequence

S(2) is the second term of the sequence

S(3) is the third term of the sequence

S(27) is the 27th term of the sequence

S(n) is just some term of the sequence

S(n-1) is the term just prior to "just some term of the sequence"

S(n-2) is the term TWO prior to "just some term of the sequence"

Fir the first example

S(n) = S(n-1) + 10

S(1) = 10

S(2) = S(1) + 10 = 10+10 = 20

S(3) = S(2) + 10 = 20+10 = 30

You show the second example.