Carnival glass has an iridescent or rainbow-like quality. The glassware was used for prizes at carnivals in the early 1900s. Many companies manufactured carnival glass. Though originally cheap, some collectors do look for certain types. Northwood is the most valuable. Look for a capital N inside a circle.
Marigold, an orange color, was the most common color. More unusual colors like red and light blue will be more valuable.
In the 1960s, many reproductions were created for the newly emerging collecting craze. These are not as in demand as the older, original versions.
Find some books on the topic and learn about your collection. There are tons of such books available online and can be quite inexpensive if you buy a used one. Once you identify what you have, then you can search prices.