Far as I know, all clovers are "annual". You can get several years out of most clover crops with a little upkeep and maintenance.

Frost seeding is a method you read about and is very simple and easy to do, but to be honest I've had a whole lot better luck getting clover established when I first did some cultivation to assure seed / soil contact.

Roundup will kill clover same as weeds. My recommendation would be to mow short and spray with roundup to kill original weeds, cultivate, then seed. After it gets growing it will have a fair amount of weeds in it. Keep it mowed to about 12" high and the clover will fill in and eliminate most of the weeds. three or four mowings a season after that will usually keep it in pretty good shape.

One thing about clover is it produces nitrogen and grasses crave nitrogen. Grasses will eventually take over a clover plot. There are some sprays that will kill the grasses only and will give your plot more life, but eventually you will need to start over. About 5-6 years is max I've gotten a nice clean clover plot to last.