Books discussing history research and writing can be found in the D13-D16 call number range. Several of these are written for students and cover finding and using primary sources. A search in GIL-Find for Historical Research - Methodology provides a number of resources.
Format impacts what you can glean from a source,
and possibly your ability to utilize it.
Professional historians often travel to use archival sources in their original format and language. This usually isn't practical for students, but bear these things in mind.
Original manuscripts may contain handwritten notes in the margins (or other useful info) that a published copy lacks.
Edited and translated works are subject to possible errors and biases of editors and translators.
Digital copies need particular scrutiny. They may contain transcription errors, may not reliably represent the original source, or may be of dubious origin (incomplete citation). After all, anyone can post something online.
Some sources may be primary or secondary;
it depends on your research topic.
You may find these in library catalogs, bibliographies, footnotes, primary source databases, library/archive websites, and Google.