Difference between FOR and AFTER triggers?

Question

There is no difference, they do the same thing.

CREATE TRIGGER trgTable on dbo.Table FOR INSERT,UPDATE,DELETE

Is the same as

CREATE TRIGGER trgTable on dbo.Table AFTER INSERT,UPDATE,DELETE

An INSTEAD OF trigger is different, and fires before and instead of the insert and can be used on views, in order to insert the appropriate values into the underlying tables.

@Ben is absolutely right.

Here is MSDN article Exploring SQL Server Triggers

A paragraph from the article:

That syntax is also acceptable in older versions of SQL Server. However, now that there are two types of triggers in SQL Server 2000, I prefer to refer to FOR triggers as AFTER triggers. Thus, for the remainder of this article I will refer to either AFTER or INSTEAD OF triggers.

Like the AFTER trigger you saw earlier, this trigger prevents changes from being made to the lastname field. However, it implements this business rule differently than the previous example. Because the INSTEAD OF trigger fires in place of the UPDATE statement, the INSTEAD OF trigger then evaluates if the business rule test passes or not. If the business rule test passes, in order for the update to occur the INSTEAD OF trigger must explicitly invoke the UPDATE statement again.

AFTER specifies that the DML trigger is fired only when all operations specified in the triggering SQL statement have executed successfully. All referential cascade actions and constraint checks also must succeed before this trigger fires. AFTER is the default when FOR is the only keyword specified.

AFTER triggers cannot be defined on views.

INSTEAD OF Specifies that the DML trigger is executed instead of the triggering SQL statement, therefore, overriding the actions of the triggering statements. INSTEAD OF cannot be specified for DDL or logon triggers.

https://docs.microsoft.com/en-us/sql/t-sql/statements/create-trigger-transact-sql