These bags are made of tough material and well welded.
The double seal at the top is difficult to seal compared to your average Ziplok baggie.
Seal one ridge at a time with your fingers paying attention to alignment.
Feel the lock snapping in place. Ignore the plastic runner, it does nothing helpful at all.
Once sealed, it's all easy. remove the knurled cap, twist the outside portion of the valve 1/4 turn and vacuum.
The instructions are not clear that the cap is not the valve.
I would have given 4 stars because of the slight difficulty of use, but the great value compared to what you find in the shops persuaded me to give it five.