What is a license
A license is an authorization to use someone's intangible property, for example software. Licenses contain crucial information about our rights and obligations, regardless of the type of license.
Always read the license!
Business-wise, each license is a type of contract we accept, which in practice means that breaching the contract involves civil liability and in some cases also criminal liability. Therefore, remember to always read the license and if in doubt - consult a lawyer.
Less is better!
In practice, the shorter the license the better (this rule works in 99% of the cases and applies to the party who uses the license). It's due to the fact that licenses always limit the rights and impose specific rules. If you're reading a long license that you can't understand it's most commonly an intentional trick that helps the rights' owner "hide" certain clauses that are very beneficial to them. Some great licenses include MIT and BSD (3-Clause).
An exception to the rule described above is a case where there is no license at all, or the license vaguely defines granting rights or waiving the warranty (for example WTFPL). We strongly discourage everyone from using software licensed under these licenses (even though they are very short) because they pose a huge legal risk.