A sugar syrup ratio of 1:1 in early spring will help them until they get enough nectar. Just mix it like you would for hummingbirds and set it out where they can get it. Give them something to land on if you put it in an open container. Charleen fixed a nice one last year for the bees in her area after the tornadoes went through there. You'll know when they have enough nectar, they'll quit visiting the sugar syrup mixture. In very hot weather they need water and plenty of it which is why they visit your bird bath. Then in late summer/early autumn they might need more sugar syrup in a ratio of 2:1 (sugar to water) to build up winter stores.
