egt probe install but what does these temp mean?!!!

hey,
i just got my egt probe installed and finished wiring up the gaugue itself, i am at idle-gauge reads 300-400degree, at ~4K rpm and the egt gauge shows me 1000degrees!! sometimes when i accelerate it will show me 1100 degrees!!

what does this all mean? the more rpm the more the heat the gauge will show. so, how do i konw that i am running lean/rich?

i am really confuse ont he usefullness of this gauge.