Can someone ELI5 this vs all of the other options? Say I have a $300k in RSUs and a handful of stocks and a 401k w/ fidelity. What does this do? Also is this

Can someone ELI5 this vs all of the other options? Say I have a $300k in RSUs and a handful of stocks and a 401k w/ fidelity. What does this do? Also is this similar to the etrade portfolio things?