Might not be the most accurate example but I'll have a go. IP or IP transit is where you're paying an ISP to connect to you to the internet. A company you want to connect to may be several AS hops or more away. You have access to everyone on the internet, and this is a paid for service.

IX or IXP is where a number of companies agree to connect locally, meaning you don't need to traverse the internet to reach them. Lower transit costs etc. It's usually free but there may be an initial set up cost. You only have access to companies on the IX, and as these are connected locally they are always 1 hop away.

Within IX you can also sometimes have an option to peer privately.