As Jason said, you should be able to immediately place a 2 in Row 4 Column 6 (r4c6) because it's the only number that can possibly go there.
You can then get a third number quite easily. Since r4c6 is 2, now look at Column 4. There is only 1 cell in that column that 2 can go. It's in Row 1, so r1c4 = 2.
To get a fourth number you will have to be familiar with a few other techniques to reduce the number of candidates that can go in a cell. You will have to understand at least pointing pairs and X-Wings.
Have a look at this site and study all the Basic Strategies and X-Wing Family.
http://www.sudokuwiki.org/Strategy_FamiliesAlternatively look at this site
http://hodoku.sourceforge.net/en/techniques.php and study the sections on Singles, Intersections, Hidden Subsets, Naked Subsets and X-Wing.
Leren