The Profile Browser shows you which color profiles are available for a particular photo in your installation of Lightroom Classic. Lightroom Classic has more profiles than earlier versions of Lightroom, so Adobe added the Profile Browser tool to enable you to organize and search them.

Profiles are important because Lightroom Classic uses them to determine how to interpret the colors and tones within a Raw file. In fact, they are so important that you should set the profile as one of the first steps in your workflow. That’s one of the reasons the Profile Browser is located in the Basic panel, and not the Calibration panel (which is where profiles are found in earlier versions of Lightroom).
For example, in the photo below the choice of profile makes a dramatic difference to the way the blue walls are rendered and the contrast.

Learn more: The 15 Step Lightroom Classic Workflow
What color profiles does Lightroom Classic have?
There are four types of color profile in Lightroom Classic.
Adobe Raw: A set of color profiles provided by Adobe. You can only apply these to Raw files.

Camera Matching: These profiles are intended to match the color treatment and tonality provided by your camera’s built-in color profiles. Again, you can only apply these to Raw files.
These are the Camera Matching profiles for Fujifilm cameras.

Creative: These are a bit like Develop Presets and let you apply creative effects to your photos. You can apply them to JPEG, TIFF and PSD files as well as Raw.

Third-party: Color profiles created by other photographers. Includes any color profiles you created yourself by converting Develop Presets, or using a tool like the ColorChecker Passport.
Tip: All the profiles in the Profile Browser are also available in Adobe Camera Raw in Photoshop and, except for some third-party profiles, the Lightroom apps for desktop and mobile.
Viewing profiles in Lightroom Classic
Use the menu marked below in the Profile Browser to choose whether to see your Profiles in a list, a grid with previews or larger previews.

When you move the mouse over a profile Lightroom previews the effect on your photo. Hold the Alt key down to temporarily see a Before version of the photo.

Click the profile to apply it to your photo. With Creative Profiles you can adjust the Amount slider to any value between zero and 200. The default setting is 100.
The photo below shows the Artistic 04 profile set at both 100 (the default) and 200 (the strongest setting).

How do black and white profiles work in Lightroom Classic?
Profiles for black and white photos work slightly differently in Lightroom Classic. When you convert a color photo to black and white by setting Treatment to Black & White in the Basic panel Lightroom changes the profile to one called Adobe Standard B&W (if you’re using Process Version 3 or older) or Adobe Monochrome (if your Process Version is set to 4 or 5).
If you apply a Develop Preset to your photo that converts it to black and white yet uses the Adobe Standard profile (i.e. one created in an older version of Lightroom) then Lightroom changes it to Adobe Standard B&W even if you’ve updated the Process Version.
If you copy and paste Black & White Mix settings from one photo to another, Lightroom only applies them to the second photo if it has a black and white profile.
How do I add profiles to my Favorites list?
Move the cursor over a Profile and click the star icon that appears to add it to your favorites.

Lightroom displays your favorite profiles at the top of the Profile Browser.

They also appear in the Profile menu in the Basic panel. This is a shortcut that means you don’t have to open the Profile Browser to access your favorite profiles.

Tip: The Adobe profiles are marked as favorites by default. You can remove them from your favorites if you don’t want them to appear in your Profile menu.
How do I use the Profile Browser to manage profiles?
If there are groups of color profiles that you don’t use you can hide them from view in the Profile Browser. Right-click on the empty area next to any set of Profiles and choose Manage Profiles from the menu to bring up the Profile Manager. Only checked Profiles are displayed in the Profile Browser.

Tip: Any profiles that you’ve marked as a favorite still appear in the Favorites list even if the group they are in is hidden.
Hopefully this gives you a good overview of the more prominent role that color profiles play within Lightroom Classic. If you’re still not sure why color profiles are so important, then my tutorial Why Lightroom Classic Profiles Matter will help.