The plural form of idea is ideas.

Is there an apostrophe in ideas?

All he really wanted to do was to form the plural of the word 'idea'. He should have just added an 's' without the apostrophe. If you'd like to know when to use the apostrophe, take a look at this excellent article (link to: Purdue OWL).

Can concepts be plural?

The plural form of concept; more than one (kind of) concept.