Simple way to explain it is: Hold your weapon down to move faster. Thats it.
Guide to Sprint
Step 1 – Clearing binds for usage
Just go to your options menu and choose the controls tab.
Clear your walking/toggle walking bind by clicking the button on the right side.
Step 2 – Setting the new “Sprinting” bind
Navigate to the Interactions tab on the controls menu.
Set the “Hold Low-Ready” action to the desired key, in this case, shift.