Accessing data on iCloud

Not enough information from you.

What "data" and for what purpose? On what equipment?

Do you have iCloud Drive set up? Do you have iCloud set up, turned on and syncing?

Set up iCloud on all your devices - Apple Support

Change which apps sync and store data with iCloud - Apple Support

Some data is accessed using the app for that data. If I want to see a contact I open the Contacts app because I have ICloud set to sync my contacts. I can see the contact on my iPhone, my Mac, or if I sign into iCloud.com and use the Contact apps there.