A cable like this; http://hosatech.com/product/cms-100/
Connect it from the mixers CR/headphone jack the the HP1 Aux input.
Very important; Be careful you do not damage your ear drums. The LD HPA1 system does have built in limiters but I would not trust that on it's own to protect your ears. It's probably designed to reduce audible distortion but is not likely to protect your ears from damage.
Set your mixer up as you would for live sound performance. Connect an MP3 player to one of the channels and get your sound going through the mixer to you normal speakers.
Turn the headphone/control room knob all the way down to start with. This is a safety measure.
Connect the cables large end 1/4" TRS (Tip, Ring, Sleeve) to the mixers headphone jack.
Plug the other end into the HP1 3.5mm TRS AUX input.
Plug your IEM cable into the HP1 output.
Hang the IEM over your ear but don't put it in your ear yet. This is also a safety measure.
Turn the HP1 Volume knob to around 1/2 way (12 o'clock)
Hold the IEM close to your ear while you slowly rotate the mixers CR/headphone knob. When you hear sound in the IEM back off the mixers CR/Headphone knob.
Put the IEM in your ear and slowly turn it up again.
Now try it with a microphone as you speak or sing. Again, start with the volume very low.
With this mixer and the simple way I explained you are going to get the same mix in the mains and in your IEM. This is usually suffice for the intended purposes of having a small mixer.
I don't currently use IEMs myself but I personally want to hear in my monitor the very same mix that is in the mains. I perform solo with vocals, acoustic guitar and backing tracks. Hearing in my monitor what is in the mains gives me confidence of what my audience is hearing. Much easier to control this way as a solo artist. Or, even as a duo or 2 - 3 singers this still makes sense to me.
When playing with a bigger band and lots of instruments it might be important to have individual monitor mixes or just vocals and a lead instrument in the monitors/IEMs.
Hope this helps.

Does the noise in your head bother me ?