They have freshman orientation for incoming members of the House and Senate. I’m not sure about what it all entails, but I know that the newly-elected members head to Washington shortly after Election Day and that’s when the orientation begins. I’m sure there is also some sort of transition process where the outgoing Representative or Senator helps out with the person coming in to replace them (much like what happens with a Presidential transition). There are also plenty of support systems, from their party’s caucus to their state Congressional delegation and down to the committees that they are assigned to.
Of course, there are certain parliamentary tricks and arcane rules that take some extra time to figure out if the Representative or Senator wants to master the legislative process and excel like some of our greatest legislators such as LBJ or Robert Byrd. It’s not a requirement to know all of those tricks (and today it’s probably just easier to hire someone who can handle that), but it certainly can come in handy when trying to pass your legislation or kill someone else’s.