what does the number under my name mean?

The number under/side your name means you have responded 6 or so topics till now. As much as you respond to any new topic, this number will increase automatically. This denotes number of responses on others topics made by you. 1 number increase for 1 topic's response. Hope your doubt is clear now. As you are new, there will be lot of doubts in future too. Better you visit FAQ, guidelines etc written below. You will find lot of important informations.

number of posts