I'm yet to play rise but the general idea with longsword is to build up spirit gauge then spam spirit guage attack to do fun anime combo. Then do it all over again. If you land a full spirit guage combo it will give a temporary damage boost that stacks a few times. This is my experience of it in world dnow how much they changed for rise
Filthy reddit link but has some advice specific to rise and sunbreak https://www.reddit.com/r/MHRise/comments/14wd2z8/tips_for_longsword/