STEP ONE: FIND AND DOWNLOAD THE HUD YOU WANT TO INSTALL (HEXHUD, ZEESHUD, SHERKHUD, ETC)
IT WILL BE A ZIP FILE YOU WILL WANT TO TAKE THE FILE IN THE ZIP FILE OUT OF THE ZIP FILE
STEP 2: OPEN UP STEAM AND RIGHT CLICK ON TEAM FORTESS TWO ON THE SIDE BAR IN YOUR STEAM LIBRARY AND CLICK BROWSE LOCAL FILES
STEP 3: CLICK ON THE FIRST "TF" FOLDER YOU FIND AND IN THAT FOLDER SHOULD BE ANOTHER FOLDER CALLED "CUSTOM" AND PUT THE FILE FROM THE ZIP FILE IN THE CUSTOM FOLDER; HOW TO INSTALL CUSTOM HUDS FOR TF2