IPFS is nice as a personal archiving tool (edit: it's not). You store a bunch of data and make it available to the public.
The problem is that no one will ever know you have that data, therefore you need a place to publish it somewhere. Gravity was an attempt of being the tool for this job.
It was a website that showcased the collections from users, and it was also a command-line client that used your IPFS keys for authentication and allowed you to paste IPFS URIs and names and descriptions.
The site was intended to be easy to run so you could have multiple stellar bodies aggregating content and interact with them all in a standardized manner.
It also had an ActivityPub/"fediverse" integration so people could follow Gravity server users from Mastodon and friends and see new data they published as "tweets".