Magis has pretty well covered it, especially making sure its a form of glyphosate only, that you apply on RoundUp Ready plants. Basically any of the generic glyphosate brands will work and is labeled for RR crops.

Depending on what is growing on the plot prior to planting, I will use 1 qt to the acre for the initial kill, sometimes 2 qt/a is required for certain weeds, before planting, if using no-till.

If planting into tilled ground, 2 to 5 weeks after planting or when the weeds reach up to 8 inches tall, I will spray 1qt/a for the first application. If things get delayed and the weeds are larger, I will apply up to 2qt/a. Under ideal growing conditions one application is sometimes all that's needed, the beans will grow together shading the ground enough weeds can't compete. Drought, hail, wind damage or poor soybean stand that slows or delays canopy closure, will likely require a second application to control late flushes of weeds, especially ragweed.

Planting RR soybeans is a very good way to clean up a plot in preparation for a perennial plot the following spring and you have the option of seeding a cereal grain or brassica into the standing beans in late summer about the time the leaves begin to turn yellow, extending the usefulness of the plot on into winter/spring.

Good luck and let us know how it go's!