GoKawiilLet's begin with Windows' built-in storage management tool: press Win + I to open the Settings panel, then go to System > Storage. Here, you'll see the total space in use on your main disk, along with a breakdown of what's taking it. Select one of these categories to jump into the relevant place and manage it.
One of the biggest hogs is likely to be Installed apps; clicking this brings you to the Settings > Apps > Installed apps page. Change the Sort by box to Size (Large to Small) to put the lowest-hanging fruit at the top. Under the three-dot (...) menu, hit Uninstall to remove anything you don't use anymore. If you have at least two drives, some programs (like games from the Microsoft Store) provide a Move option.
The Temporary Files category shows several checkboxes for items like Thumbnails that can be easy space-savers. Click Cleanup System Files to show more types of clutter. Be careful with Downloads and the Recycle Bin — while those spots can use lots of space, you might not want to delete them outright. It's best to open the Recycle Bin from your desktop and quickly check for anything you want to restore, since clearing the bin permanently deletes the files in it. Similarly, you might have items you want to save in your Downloads.
If you have multiple storage drives, back on the Storage page, expand the Advanced storage settings section and choose Storage used on other drives to see the same breakdown for the others.