Will give you every record that has an instance of "abc" starting the field off. So it would give you records with "abc" and "abca" and "abxc2342riojfosjdf34kj" occuring in that field. By putting a wildcard on both sides, you would get every record with "abc" anywhere in that field. And so on. Experiment!
By putting in a parameter, the query will prompt you for input.
Like [Put any text you want here barblogon except for punctuation]
When you run the query, a pop-up will appear with "Put any text you want etc.", and a blank. If you type "abc" into the blank, you'd get every record with "abc" for that field.
By putting wildcards on either/both sides, you can then narrow/widen your seaches.
Experiment! (And let us know how it works out for you!)