{ downloading from dafont.com }

go to the website: www.dafont.com

find a font you want and download

click on the .zip (or the font that you just downloaded) and this should pop up.

at the top left in my downloads folder, you can see the font. to install it in your font book, double click on the download

click install at the bottom right

at there you go! after that, you can find it in photoshop, and i believe in other programs such as: imovie and final cut pro.

{ downloading from a font pack }

i find font packs on www.deviantart.com. 

search 'font pack' into the search bar

click on the one you want and find the download button

it's at the bottom right in the picture above

click on the download and a folder should pop up in your downloads. click on it and you should have all of the fonts listed in the font pack.

click on the font you want installed, click install font, then it should show up in your font book (basically follow the last three steps from the first part, downloading from dafont) and you're done!