To route tracks through a bus:
1. Create an empty channel called Drum Bus
2. Control-click to highlight all of the channels you want to send to it
3. Click and drag the highlighted channels so that your mouse cursor is positioned over the Drum Bus channel. Watch the blue line that indicates where it's going to drop the selected channels. You'll see that the line is fully to the left when your mouse cursor near the top/bottom of a channel, and it indents slightly to the right when your mouse is over the middle of the channel. You want the line to be indented under the drum bus channel when you let go of the mouse button so that it drops all of the drum tracks as children of the Drum Bus, which now becomes a collapsible a folder. Audio is automatically routed through the Drum Bus (parent folder) prior to the master bus unless you un-check "Master send" in the i/o dialogue box of a child track (labeled "route" in the newest version of Reaper), and then you can choose the desired destination via the "Add a new send" drop-down in the same dialogue box, or via the routing matrix (alt-r).
To create an effects send/return:
1. Create a blank channel called "Reverb"
2. Insert your reverb plugin of choice, 100% wet
3. To send your Snare (in parallel) to the reverb, you can do one of the following:
a. click and hold the "i/o" (aka "route") button of the "Snare" track, and drag it to the "Reverb" track and let go. You will get a send parameters dialogue box where you can adjust the send level, panning, etc.
b. click the i/o (route) button on the Snare channel, pull down the "Add a new send" drop-down, and select Reverb.
c. Click the i/o (route) button on the Reverb channel, pull down the "Add a new receive" drop-down, and select Snare.
d. Press alt-r to bring up the routing matrix. Find "Snare" in the vertical axis, and "Reverb" in the horizontal axis. Click on their intersection, and adjust the level.