Many straps, including just about all of our Mac's straps, arrive pre-threaded onto the ratchet (our Tire Block Straps and UTV Nets are the exception). Should your webbing slip out, there's how to thread the strap properly from a professional, as well as a brief step-by-step outline:
Step by Step

Step 1. Thread webbing through mandrel

Step 2. Pull a large amount of the excess through

Step 3. Lay the excess over the webbing so both layers are flat

Step 4. Operate the ratchet handle to start tightening the webbing up
With the ratchet threaded, you'll be able to hook up your end fittings to your anchor points and ratchet up the rest of the slack for a tight, properly-tensioned secure strap.