Open up a .psd in 150x150
find an appropriate image and add filters (google how to add them if you don't know how)
add a font that looks nice, you can find them on dafont.com or from any other site
and for what makes an emblem an emblem, the little diagonal lines;
http://i.imgur.com/ubV7BCs.png
make a new .psd doc, width 8, height 8 and zoom in to 3200% and press ctrl + i (inverts colors so you can see the border lines)
using the pencil, fill each square diagonally like this;
http://puu.sh/gkxv6/cdb1553f7e.png
press ctrl + i again so the dots are black and it looks like this;
http://puu.sh/gkxxU/7f9a8ae76a.png
now edit > define pattern > and name it whatever
on your emblem that you've made click edit > fill and use these settings
http://puu.sh/gkxCs/61055a209c.png
it gets easier as you go, you can't make professional ones straight away so if i were you, i'd stick to simple