I cannot resist posting this.
1- Sql Injection is explained better in one cartoon, than most other documents.
2- Mostly it does not do much to the server, but only to the underlying data. Consequence include delete, insert , select records, drop, create tables. (based on permissions etc..)
3- Examples.
4- Sorry I do not know PHP. But as long as you can abstract your DB layer from your View, you should be fine.
