An appendix or appendices are usually the last pages in a document/project. They contain things that you did not have space for in the main part of your project.
For example, imagine halfway through my project, I was discussing the increase in the population between the years 1990 and 2000. If I had a table that showed all the relevant information, but the table was too long to include in the middle of my project, I could just say: See Appendix A for a breakdown of population growth between the years 1990 and 2000. Then, at the end of my document, the first appendix (Appendix A) would show a table.
We use appendices for many things: tables, figures, permission to use premises letters, informed consent forms, etc. Basically, anything that is relevant to your project but would not look good stuck in the middle of your text.
There are two main ways to layout your appendices: You can place the heading (Appendix plus letter) on a blank page and place your information (e.g., table) on the next page, or you can place the heading at the top of a blank page and add the information directly below.
Hope this helps!