Info on cookies
Judging by your question I'd suggest you probably need to spend some time researching what cookies are, how they work and how they are used. I'll answer this question, but the answer may not make that much sense to you unless you understand the context.
Cookies are transmitted in HTTP headers in plain text, so you can read them with a text editor if you want, but common ways to read them as part of the HTTP session are to use an intercepting proxy or some sort of browser extension (Cookie Safe, Add and Edit Cookies, etc). You can also grab persistent cookies from disk.
Removing encoding or encryption will be application specific, and while there are some common standards for doing this (e.g. Base64), you really need to know how the associated web application generated them or you will need to reverse engineer the encoding/encryption yourself (perhaps using some good guesswork based on those common standards mentioned earlier). Encryption can also be performed at the protocol level (e.g. https), in which case you need to decrypt that before you can access the cookies.
Emulating cookies is done by just copying them using an appropriate method. Use an intercepting proxy to insert them in (more efficient if you use a Set Cookie directive in the modified response from a server), or use a Cookie editor to add them at the browser.
Edit: For anyone else coming across this thread a really good reference for learning about cookies is here.
