Anyone unfamiliar with chainsaws, even those using small electric ones at home should read basic advice on using them, I've known someone become permanently disabled by trying to be butch with one, making a fundamental error and coming severely unstuck. It wasnt the saw did the damage, but the tree and cutting it the wrong way. Stihl's manual's open with some simple rules, have a look at any;
http://www.stihl.co.uk/owners-manuals-safety-brochures.aspx?spm=MS&Search=#Dangers to look out for that you may be unaware of are;
Leaning trees; these are the hardest to deal with. Look for the likely compression points, if they spring up in a direction you haven't anticipated they can really fly back at you and cause major damage. Also think carefully where they are likely to fall, they can go sideways as well as down.
Escape routes; once a cut tree starts to move, whether its standing, leaning or on the ground you want to be well out of the way, and have your path away from the tree clear. Dont clamber over debris to get to the tree, get rid of it all first so the work area is clear.
Wear the vizor down. A small twig flying back at you at speed could take out your eye. Watch out for old wire, if the saw hits it, it can snag, kick back and fly at you. Try to stand at the side of the blade rather than directly behind it, or it can fly up and catch you. Always contact the tree with the edge of the chain bar, not the tip, again that can make it fly back.
Avoid contact with debris on the ground which can fly back and give you a painful whack, and dont touch the soil, it'll rapidly blunt the saw.
Watch out for roots which you can trip over. A good footing is essential.
Always have a mobile in your pocket.
Sure you want to try this without training?