The Basics of SQLi

SQLi (SQL Injection) is used to exploit the security of a website using SQL. The vulnerability is present when an input either incorrectly filtered for string literal escape characters or when an input is unexpectedly executed.
The architecture of a site if broken down like this: Site -> Database -> Tables -> Columns -> Data.
 So in order to get to the data, you must start from the top and work your way down. It's your job, to find the hidden data somewhere in the area (site) and it's your job to find that information using queries.
You goal is to get the admin login credentials.

SQL (structured query language) is a programming language designed to manage the data inside a database. The database contains tables, the tables contain columns, and the columns contain the data. Queries are known as commands and are used to access the database.