Index Register?

[laxonator]

I have created a string the following way:

.data
STRING1: .asciiz "76543210"
.text

How do I access each byte of this string? I would like to load each byte into registers and then run tests on each byte. I'd use something like this:

lb $s0, 0(--What goes here?--) # load '7' into $s0
lb $s1, 1(--???--) # and so forth

What do I do? Please help! I am new to assembly and kinda confused.