There's good info here:
Thread: GLPFAQ How do I post pictures in a thread?

As a paid member, you can upload your own "custom smilies". Then, you can access these directly from the "post entry" page. You'll see them just above the "Pictures" icon lists.

Otherwise there's a shortcut. GLP has literally 1000's of available smilies (that other members have previously uploaded). You can display ANY of these in your own posts (as a blue name) by textually inserting the corresponding smilie code.

The trick is knowing the smilie's name. For example, consider this one:



It's typed like this:

: clintyes:

without that space after the first colon.

A couple of years ago, I did an extensive thread (with the help of many others) to reveal categorized lists of available smilies. However, as the thread grew to more than 4000, it now takes about 3 minutes for the thread to fully load.



Nonetheless, you can take a gander here:
Thread: GLP APPENDIX: 4500+ Categorized SECRET Smilies