Hi, and welcome.
The available balance is the real WEBD you own.
The potential, as the name says, is only a rough estimation, and is not guarantied to transform in available.
To get constant payments you need to have considerable CPU power and only mine in a pool that does have enough miners to catch POW blocks. Here you can check in the pie graph winch pools catch winch kind of blocks: https://www.webdscan.io/stats

But easiest way to mine is to just buy some WEBD from exchanges and then stake it (POS mining).