Searing beef before slow cooking can help the beef turn out better when slow cooking the beef and will make the beef cook faster in the slow cooker.
But if you don't want to sear the beef before slow cooking you don't have too.
I usually just add the beef to the slow cooker and let the slow cooker do all the cooking and the beef turns out just fine for me.
Raw meat can be cooked in a slow cooker and as the slow cooker is cooking the other foods the meat will also cook.
I usually never cook meat first before putting it into the slow cooker and it's always cooked the meat all the way through.
I will sometimes make beans as well as ground beef added to the beans and just place the ground beef into the slow cooker along with the beans.
The ground beef when raw cooks just fine along with the beans.
You can cook the raw meat first before slow cooking it but the slow cooker will cook the raw meat which is the point of a slow cooker.
Just add the raw meat and any other foods and after 8 hours or so the food will be cooked and ready to eat.