The EAS FC Catalogue can be found on the "Home" screen from the main menu (use

or

from the "Main Menu" to move to the "Home" screen). Use the

,

,

, or

to highlight the "Catologue" tile, and press the

button to enter the Catalogue.
Use the

or

buttons to highlight either the "Ultimate Team" or "All Items" tab, then select a "FUT Loan Player", and press the

button twice to redeem.
The most inexpensive FUT Loan Player, as of the date this solution was written there are several players who can be purchased for loan at the cost of a cool 500 FCC (Football Club Coins) - just find one of those and take your pick if you are hurting for FCC.
Conversely, if you don't have that many coins yet, go play a bit of FIFA and you soon will.
Alternatively, you can access the EAS FC Catalogue by pressing the Start button

on the Xbox controller (assuming you are on a screen where the quick menu is accessible), then using the

or

to move over to the Catalogue menu - the menu is represented by a yellow shopping cart icon.
Then simply use the

and

buttons until you get to the FUT Loan Player you wish to sign, then press the

button twice to redeem.