AJAX for displaying custom posts

Hi,

I need a little help as I am going round in circles,

I have a site we have developed where we made some plugins which use custom post types to provide an area for the client to add in various posts / articles which are different to the rest of the site, basically lets say for example an FAQ or News section, they are able to add in a load of posts which will sit under the appropriate section

What I need to do is to create a form on the front end of the site which will list set custom posts types in a drop down (these will be hard coded in) – then I need a submit button that will once pressed show all the posts for that custom post type.

I want these to change without loading the page so I am looking at using AJAX but I am really struggling to find working examples of how I can achieve this. I haven’t developed with AJAX much in the past. I need it to be fairly secure so I need to integrate nonces into it,

can anyone help and point me in the right direction? I know there is loads about ajax an wordpress on google but i seem to have been through every page and am getting nowhere.

thanks in advance.
J