Hi Candice, UASF stands for User Activated Soft Fork whereas UAHF stands for User Activated Hard Fork.

As an example, let's say you have 1 BTC and you store it on Bitfinex, an exchange that supports both chains, then you see something like this in your account balance starting from July.

BTC : 1.00000000
BTC-Old : 0.00000000
BTC-148 : 0.00000000

You will be given the option to continue trading BTC as usual for a limited time. Or, convert (split) your BTC and trade on both chains. Assuming that you opt to convert, then your balance will look like this.

BTC : 0.00000000
BTC-Old : 1.00000000
BTC-148 : 1.00000000

Hope this helps.