There are several methods sometimes it is rather simple, at others it takes several scientific techniques to determine. The easiest being relative dating which is implemented by looking at surrounding finds, and geological features. By looking at finds and dating those and being able to date in relation to these finds. And by looking at geological features you are able to understand a general time of burial. This has been done in the field with success in cases like that of a viking burial in York. This burial was able to be dated by Archaeologists based on the metal finds, like jewelry and small weapons. To explain this the source that explains this the best is and article in the Journal of Field Archaeology titled Distinguishing between Artifacts and Geofacts. This article helps to explain the positive effects and issues with using geological data as a method of dating. Where finds are unavailable there are forensic methods which provide Absolute Dating, that involve looking at teeth which hold evidence of what the person ate regularly, where they were from, and how old they were. While also being able to use carbon dating, which is common in osteo-archaeology but can still be used. The sources Handbooks for Archaeologists: No 3: Radio Carbon Dating, authored by Mook and walterbolk and an article in Archeological Method and Theory, titled Radio Carbon Dating, help to better explain why Radiocarbon dating is such a good resource for dating. I hope this answers your question and I apologise for not using quotes but to understand how these methods are used I would need to use large swaths of these mentioned material.