Custom posts types and role capabilities

Hi (excuse my english please)

I’m trying to create an academic website where users can publish their wokrs and papers, etc.

I’m using custom post types to do this (works, papers, studies, etc).

So, i need to know how can i restrict their permissions to only add custom post types contents (papers, studies, etc) and NOT edit or add normal posts or pages.

I hope somebody can help me with this.