These suffixes added to a verb root make the action one that involves two or more people.
atmaq - to throw; atışmaq = to exchange fire
görmək - to see; görüşmək = to see each other; to meet up with each other
gülmək - to laugh; gülüşmək = to laugh all together
vurmaq - to hit; vuruşmaq = to fight; to have a fight
yazmaq - to write; yazışmaq = to correspond with; to write letters to each other
yığmaq - to collect; yağışmaq = to assemble; to gather together