Hello Ankit,
There are basically two types of triggers.
1. Before triggers are used to update or validate record values before they’re saved to the database.
2. After triggers are used to access field values that are set by the system (such as a record’s Id or LastModifiedDate field) and to affect changes in other records. The records that fire the after trigger is read-only.
and there are following types are events in triggers –
1. before insert
2. before update
3. before delete
4. after insert
5. after update
6. after delete
7. after undelete