My hair is nice & long but it seems to go rough at the bottom. Whenever I brush or wash it, I find about a few of strands of my hair falling down. I am 13 and worried about my hair's health in the future. Can I get some advice about it?

Your hair is rough on the ends because the ends are probably split. 
The ends of your hair are old and become drier than the hair at the
roots, so it is important to keep them trimmed regularly.  Also, it is
normal to lose 75 to 100 hairs per day, so just losing a couple is not
of concern.