Opening and closing jump rings is most likely to be the most used technique in jewellery making, and it's a really important one to get right. Having neat, secure jump rings is integeral to the aesthetics and function of each jewellery piece. Luckily it's also probably the easiest technique to learn as well.
The best pliers to use are either chain nose, bent chain nose or flat nose pliers. You need a plier with a flat section so you can get a good grip on the jump ring (I have used round nose pliers in emergencies... no biggie). It's also pretty useful if you have two pairs (one for each hand) which gives you added control and keeps your nails intact! But if you only have one pair you can use your thumb and finger to do the same job.
It's best to grip the jump ring across as much of one side as possible. This gives you maximum control when using the other plier/hand to open the other side. Pull the other side towards you (or push it back). Don't open the jump ring by pulling the two sides apart in opposite directions. Doing this will bend the ring out of shape!
Once you have used your jump ring, close it back up again moving the ring back into shape.
To strenthen the ring and ensure it is tightly closed up push the two sides gently together whilst moving them back and forward.
And that's how to open and close a jump ring. Don't worry if it seems a little tricky at first. It takes a bit of practice to perfect, and I promise after a little time you'll be making perfect jump rings automatically!