Web addresses can only contain a limited set of characters, so spaces become %20, “&” becomes %26, and so on. Encode text to put it safely in a link, or decode a messy link to read what it really says.
A value inside a link is the usual choice: a search term, a name, or another web address you're passing along as a parameter. Everything that could confuse a browser is encoded, including / ? & and =.
A whole link keeps the characters that give a web address its structure, and only encodes things like spaces and accented letters. Use it to clean up an address you're about to paste somewhere.
Plus signs are how web forms send spaces (search?q=hello+world). Turn on "Spaces as +" when decoding form data, or plus signs will stay as plus signs. When you decode a full link, we list its parameters and point out tracking codes you can usually remove. Everything runs in your browser.