You can brown the meat some before slow cooking it but it's not required.
When cooking meat in my slow cooker I just throw the ground beef or other meat into the slow cooker and cook it all night or all day while away from the house.
Then usually 8 hours later when I wake up or return home from doing errands or return home from work then the food and the meat is fully cooked and ready to eat.
If you like the meat browned before cooking then it won't hurt anything to brown the meat a bit before slow cooking it but you don't have too as the slow cooker will slow cook the meat.