Macro for random numbers from range when conditions are met

Hi, I do not have any knowledge about macro, but I think can't avoid using one this time. In my "Staff" sheet in column G I need (not repeating) random number form column B "terminal" sheet (B2:B300) if cell next to this number (column C) is empty. Them random numbers can only by assign to Column G if in Column H is word "pick" or "rec" next to them. Number need to stay the same untill word from Column H will not gonne be removed. Then, this number can be use again. This is how it's looks like:
"Staff" sheet "Terminal" sheet
Column G Column H Column B Column C
2 number here pick W205
3 W207 log
4 number here pick W215 missing
5 rec W216
6 desp W217
7 put W201
I appreciate all the help because I've been working on it for 3 days without success