There are two basic classes of sealers to choose from. The first are penetrating sealers. They generally do not require any concrete prep beforehand unless you have a very smooth or power troweled concrete surface. Penetrating sealers do exactly as described - they penetrate the surface of the concrete upon application.
Unlike a coating, they do not form a film at the surface. Instead, they all have varying reactions with the minerals in the concrete to form a molecular barrier right at the subsurface. As a result, they do not change the color or texture of the concrete. This is why they are non decorative.
Depending on the type of penetrating sealer used, including the profile (texture) and porosity of the concrete surface, they can do a good job at resisting moisture intrusion, and road salts as well as provide a decent amount of stain resistance. Some are better than others. None will provide 100% resistance to moisture intrusion or stain resistance. Moisture, chemicals, and petroleum products left to sit will stain the concrete to some degree unless cleaned up in a reasonable amount of time. They do make cleanup much easier though than unsealed concrete.
Penetrating sealers are also the easiest to apply and usually the least expensive of options. All they require in most cases is a pump up garden sprayer to apply the sealer to the surface. One of the more popular penetrating sealers as mention earlier is GhostShield. It's actually a system of sealers and is more expensive than a one application option. You can learn more about it in the link below.
https://allgaragefloors.com/oil-repelling-concrete-sealer/
The other type of sealer is a coating. Coatings are film forming and actually prevent (seal) moisture, petroleum products, and chemicals (depending on the coating) from reaching the concrete. They are available in clear and colored tints. They are considered decorative since they change the appearance of the concrete. Clear will darken the surface slightly and provide a glossy appearance in most cases. They can also be slippery when wet unless an anti-slip additive is added to the final coat.
Coatings are the easiest for cleaning up spills and general cleaning maintenance in general. Examples of coatings would be epoxy, polyurea, polyurethanes and polyapartics. Acrylics coatings are another example, but they are not as durable as the those previously mentioned and some acrylics are susceptible to chemicals.
Most coatings are highly resistant to staining, even if the chemicals and other petroleum products are allowed to sit for long periods. If staining does occur, it's the coating that stains and not the concrete.
Coatings are also more expensive than penetrating sealers and most require prepping the concrete first via etching or grinding. Unlike penetrating sealers, coatings can also get damaged. Sharp heavy objects that scratch them is the most common. Other examples are burn marks from welding or chipping from heavy objects dropped on the concrete. Of course, how much they resist this type of damage depends on the quality of the coating or the coating system (multiple coats).
One of the more popular coatings for DIY application and excellent protection are the single-part polyureas. These are arguably the easiest to apply, but they still require concrete prep beforehand. A single coat of a clear polyurea makes for excellent protection from stains and chemicals as well as easy clean up. You can read more about these type of coatings in the link below.
https://allgaragefloors.com/polyurea-best-garage-floor-coating-kits/