There are certain tools that are used throughout this site. Before you begin, it would be good to download, install and become familiar with the following.
Notepad++ is a useful text editor that allows more flexibility than what comes with Windows (Notepad). Some helpful features:
Easy to switch files from Windows to Unix line endings.
Extensive regular expression support.
Powerful ways of searching across multiple files.
Diff capabilities (see the difference between files).
Kdiff3 allows you to easily see the differences between two files, and makes it possible to create a third file by iterating through the diffs and picking which version should "win".
Solid is a tool for validating the structure of an SFM file. Also allows making a number of changes that may be needed in the Validate Structure phase of the import process.
It will also help if you are familiar with regular expressions (regex). It is beyond the scope of this site to teach regular expressions, but below are some helpful links.
A valuable site for practicing and learning about them is https://regex101.com
Another valuable site for looking up regex syntax is https://www.regular-expressions.info/
A good YouTube playlist for a series of lectures on regexes is
https://www.youtube.com/watch?v=7DG3kCDx53c&list=PLRqwX-V7Uu6YEypLuls7iidwHMdCM6o2w