First go to Widgets Toolbars and make sure Tool Options is activated, eventually activate/deactivate it some times to identify were on the screen it is located. Once you know where to look for the distance box, go for offset:
2 ways to use offset:
a) select first the entities to be offsetted, then check offset, the distance box appears instantly in the tool options bar.
b) check offset, then select the entities, you must hit Enter to activate the selection, the distance box will not appear until you hit Enter