The recursive formula
[tex]a_n=a_{n-1}+5[/tex]
means that the current element ([tex]a_n[/tex]) is written in terms of the term immediately before ([tex]a_{n-1}[/tex]).
In order to get [tex]a_n[/tex], you have to add 5 to the previous term [tex]a_{n-1}[/tex]. In other words, every term is 5 more than its predecessor.
So, if we want the 8th term, we can keep adding 5 until we get there:
[tex]\begin{array}{c|c}n&a_n\\1&3\\2&8\\3&13\\4&18\\5&23\\6&28\\7&33\\8&38\end{array}[/tex]