To begin scrolling you need to press Ctrl-b + [ ,assuming Ctrl-b is set as the prefix, and then use the arrow keys (or hjkl if you use vi mode) to move around.
To scroll a little bit faster you can use the following, adding the key bidings for vi mode as that is what I use.
| Function | Key Combination |
|---|---|
| Half page down | C-d |
| Half page up | C-u |
| Next page | C-f |
| Previous page | C-b |