Tabooti, deekay, be helpful to the young people. Lol.
You do not download opticraft, you put the server ip into multiplayer on minecraft.
1:Open minecraft
2:Put in your login information and click login
3:Click multiplayer
4:Go to add server
5:Enter opticraft as the name
6: The ip is: smp.opticraft.net
7:Click done and click on the server
8:Hit join server
9:Follow the rules. We have a zero tolerance for rule-breaking
Edit:Ninja'd by pen :p