For front wheel drive cars fitting to drive wheels only would normally be sufficient, covering both drive and steering requirements. For rear wheel or all wheel drive fitting to all wheels may be prudent.

just the drive wheels and there are two chains in the box. (so 2 sets if you driving 4WD)

2 chains in the box, just for the drive wheels (you may need 2 sets if you have 4WD)

Look under Travel & Touring, then Snow Chains bottom of first column.

Check with vehicle manufacturer, there are factors other than simple tyre size to be considered.

Snow chains can be used on snow free patches over a short distance, a couple of miles should be OK. However the driving speed should be reduced substantially (20 mph) as traction is severely reduced, hence the stopping distance increased. In the event of an accident whilst on chains on snow-free roads, insurance cover may be invalidated.