I'll make an assumption here, you both have manuals for your Tx's.
Expo is short for exponential. What this means is that you can adjust the amount of throw in any given plane, relative to the amount of stick movement. You can for instance, on the 9 CHP, program a curve so that the first little bit of stick movement has only a small effect on the relative servo, but as you move the stick further the movement of the servo increases at a greater rate than the relative stick movement. To get the best idea of how this works it's a lot easier to have a Rx and servo hooked up and to just play either these settings to get the idea into your head. But, for a sim it's not unusual to set these to 0.
Now as for Revo tail mixing. This is a programable (again - hence the manual!) mix in the Tx. What this is about is that if your heli has only a cheap or mechanical gyro in it, for stabilizing the tail, you need to be able to increase the pitch of the tail blades at the same time as you apply more Collective pitch. This is to counter the extra torque from the main blades. The more expensive or modern gyros can do this on their own. Again you need to turn off (INH - Inhibit) any pre set mixes in your Tx for the sim.
This is the bit I always get wrong!
Mode 1 is where the Collective (throttle and Collective pitch) are on the Right Hand stick and Cyclic (Cyclic pitch - tip the heli forwards and backwards, Ailerons - tip the heli Left and Right) is on the Left hand stick. Most of us however fly mode 2, the other way round. Most of the Tx's also come in configuration 2, Collective on the Left Hand side. The gimbals in the Tx are set up for that, the Collective quite often having a click stop action for Throttle and Pitch. Ohh the Collective also has Left and Right function for the Rudder, this is the pitch of the Tail blades.
Hope this is of some help