How come Mootools work but JQuery doesn't?

i a kindda bit confused,
at the time I enabled any modules or plugins using JQuery, then the rest of
the other tools who just use Mootools get dead...!

I wonder, is there anything make it conflict as always?

How about this forum anyway? Does it just using MooTools or also the JQUery as well....?

Uh, oh.