I don't have one of these mixers but in reading the manual this procedure looks pretty straight foward.
1) Press the AUX 1 display button on the left side of the mixer.
This will show the current routing status for the AUX channel. The default is
all channels sending on all AUXs, but this has probably been changed if the mixer has been used very much in the past.
2) Select Channel 1 using the "Sel" button above Ch1 fader
3) Press the Aux 1 button from the "Selected Channel" buttons on the right side of the mixer
4) Press the "ON" button at the bottom of that group of buttons
5) Press "Enter" to toggle pre or post fader send
6) Press the Aux 1 button from the "Selected Channel" buttons on the right side of the mixer again and adjust the send level using the "Send Level" knob
You should now be sending Ch1 on Aux 1. Be aware that you are probably sending several other channels on Aux 1 also and may need to turn those sends off depending on what you are tying to acheive.
All the info you need for a given send is in Aux display so you may want take
some time to become very familiar with this.
The Aux display tells you the status of the send. To enable or disable other
channels sending on the Aux press the desired Aux button then the Ch button.
Press the "ON" botton to toggle the send on or off.
This is the version of the manual I'm referencing (starting on p42)
http://www2.yamaha.co.jp/manual/pdf/pa/english/mixers/02R1E.pdf
Good luck
Erich