Johnny Saldaña has published a number of books and articles on qualitative coding. They describe a code as:
...most often a word or short phrase that symbolically assigns a summative, salient, essence-capturing, and/or evocative attribute for a portion of language-based or visual data.
What kind of data can you code?
The data can consist of interview transcripts, participant observation field notes, journals, documents, open-ended survey responses, drawings, artifacts, photographs, video, Internet sites, e-mail correspondence, academic and fictional literature, and so on.
You may notice when reading ethnographies that authors may not describe how they analyzed their qualitative data. In certain disciplines, this transparency is expected, while in others it may be seen as too much to mention in a methodology section.
As a result, you may be able to find information about coding strategies in academic articles in your area, but this is not a guarantee.
You may need to be creative in your searching:
If you have a large dataset or you are working with many collaborators, you may be interested in software and browser applications designed to aid qualitative research.
The resources below discuss Computer-Assisted Qualitative Data Analysis Software (CAQDAS or QDAS). QDAS has become popular among social scientists, but that does not mean it cannot be useful for those in the humanities or in STEM.
Remember, all technology comes with a learning curve! Only tackle new technology if you think it will really help you. Most scholars still code traditionally using printed documents and/or by highlighting and notating digital documents with whatever word processing software they have.
This video introduces qualitative coding. It provides visuals for the commercial CAQDAS package Quirkos, but the information is applicable no matter what method you use to code.
This video shows a very traditional way of coding: highlighting, cutting, and organizing.