Appendices (plural) go at the end of the document as an 'appendage'. It is generally assumed that there are multiple appendices, so the first heading is 'Appendices'. After this, the headings adopt outline numbering with an alpha prefix for each Appendix (singular).
It is advisable to consider what the headings will look like in a Table of Contents; so 'Appendices' are generally at the same heading level as a 'chapter' (or major section).
|2||Appendix A. Name||First appendix|
|3||A1. Heading Text||Sub-section|
|4||A1.1. Heading Text||Sub-sub-section|
|5||A1.1.1. Heading Text||Sub-sub-sub-section|
|2||Appendix B. Name||Second appendix|
|3||B1. Heading Text||Sub-section|
|4||B1.1. Heading Text||Sub-sub-section|
|5||B1.1.1. Heading Text||Sub-sub-sub-section|
If you have only one appendix, then the 'Appendices' heading is not required.