In the sling package there should be four items. 

1. Sling (Frontend of the sling has the cam lock buckle)

2. Front handguard sling adaptor

3. Attachment extender

4. Buttstock adaptor

Attaching Sling

Not all pieces are needed depending on the type of buttstock and handguard you have on your rifle.

Attaching sling to the buttstock:

If you are using a traditional M4/AR15 collapsable buttstock you can eliminate the use of the buttstock adaptor (#4). Most M4 buttstocks have a slit opening towards the middle rear of the buttstock (See image below). This is where the first anchor point of the 3 point sling can be looped through. Loop the rear of the sling through the slit and around the stock, then secure it by slipping the nylon through the triglide.  This will keep it locked into place.

 Here we used an HK 416 style buttstock as our anchor point for the 3 point sling (see image below). 

Example of other buttstocks used with the buttstock adaptor (#4)

 Attaching sling to the front handguard:

 There are various handguards on the market. Some handguards have attachment point slits to eliminate the use of the front handguard sling adaptor (#2) and the one inch attachment extender (#3). If that's the case you can attach the front portion of the sling directly in the same manner as with the M4 buttstock. If your rifle does not have attachment points (such as the quad rail handguard pictured) you can use either handguard sling adaptor (#2), one inch attachment extender (#3) or both depending on the width of the handguard.

One inch attachment extender (#3) used as attachment point

 After your rifle's buttstock and front handguard have anchor points and the sling is attached, you're ready to go.

Learn more about the 3 Point Sling

Here's a quick user guide