The official servers were shut down on October 3, 2022.
Overwatch features squad-based combat with two opposing teams of six players each. Players choose one of several hero characters, each with their own unique abilities and role classes. The four character roles include: offense characters with high speed and attack but low defense, defense characters meant to form choke points for enemies, support characters that provide buffs and debuffs for their allies and enemies respectively (such as healing or speed alterations), and tank characters that have a large amount of armor and hit points to withstand enemy attacks and draw fire away from teammates.
Source: Wikipedia, "Overwatch (video game)", available under the CC-BY-SA License.