Which files?

You can either use files to be explicit:

{
    "files":[
        "./some/file.ts"
    ]
}

or include and exclude to specify files. E.g.:

{
    "include":[
        "./folder"
    ],
    "exclude":[
        "./folder/**/*.spec.ts",
        "./folder/someSubFolder"
    ]
}

Some notes:

if files is specified, other options are ignored
**/* (e.g. sample usage somefolder/**/*) means all folder and any files (the extensions .ts/.tsx will be included and even .js/.jsx if allowJs is true)

Which Files?