What is this about Biden wanting to tax us on unrealized capital gains (how much our stuff has appreciated in value)?

This is an issue that I’ve been hearing a lot of rumbling about, but there just doesn’t seem to be any clear cut answers, even with all the stuff I’ve read. <br><br>Can someone explain this in a simple way? Like, what do they think is going to happen if they do this, especially as the economy is in a downturn already?