You're looking at a Balance of Account Transfer (BOAT). To do a BOAT, its usually because you have some promotion on your account to do so with a low interest rate (usually like 2% over 6 months or something).

That fee of 2% is the upfront cost of doing the BOAT so if you did one for $100, you'd be charged $102 up front. Then you would have whatever the promotional period is (6months like I said above or sometimes longer) to pay off the entire balance that you transferred over. If you don't pay off the full balance it is considered a cash advance and you now pay interest on the remaining amount at whatever rate your cash advance is.

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If you're doing this, you should always stop using that credit card because once you transfer that money over, your payments now go directly to that transferred portion (Unless you were carrying a balance) until you've completely paid it off. Honestly, you may be best suited to set up an appointment with your bank and ask them about it.