guide: begin How To section

content/docs/command-reference/add.md

@@ -59,6 +59,9 @@ files that can be easily tracked with Git.
 It's possible to prevent files or directories from being added by DVC by adding
 the corresponding patterns in a [`.dvcignore`](/doc/user-guide/dvcignore) file.
 
+You can also [undo 'dvc add'](/docs/user-guide/how-to/undo-adding-data) to stop
+tracking files or directories added previously.
+
 By default, DVC tries to use reflinks (see
 [File link types](/doc/user-guide/large-dataset-optimization#file-link-types-for-the-dvc-cache)
 to avoid copying any file contents and to optimize `.dvc` file operations for

content/docs/sidebar.json

@@ -98,7 +98,12 @@
           "katacoda": "https://katacoda.com/dvc/courses/examples/dvcignore"
         }
       },
-      "updating-tracked-files",
+      {
+        "label": "How To",
+        "slug": "how-to",
+        "source": false,
+        "children": ["undo-adding-data", "update-tracked-files"]
+      },
       "setup-google-drive-remote",
       "large-dataset-optimization",
       "external-dependencies",

content/docs/user-guide/how-to/undo-adding-data.md

@@ -0,0 +1,46 @@
+# Undo Adding Data
+
+There are situations where you want to stop tracking data added previously.
+Follow the steps listed here to undo `dvc add`.
+
+Let's first add a data file into an example <abbr>project</abbr> using
+`dvc add`, which creates a `.dvc` file to track the data:
+
+```dvc
+$ dvc add data.csv
+$ ls
+data.csv    data.csv.dvc
+```
+
+Now let's reverse this action:
+
+> Note,if you are using `symlink` or `hardlink` as
+> [link](doc/user-guide/large-dataset-optimization#file-link-types-for-the-dvc-cache)
+> type for DVC <abbr>cache</abbr>, you will have to unprotect the tracked file
+> first (see `dvc unprotect`):
+>
+> ```dvc
+> $ dvc unprotect data.csv
+> ```
+
+You'll need to remove the corresponding `.dvc` file and `.gitignore` entry using
+`dvc remove`:
+
+```dvc
+$ dvc remove data.csv.dvc
+```
+
+Data file `data.csv` is now no longer being tracked by DVC.
+
+```dvc
+$ git status
+    Untracked files:
+        data.csv
+```
+
+You can run `dvc gc` with the `-w` option to remove the data that isn't
+referenced in the current workspace from the cache:
+
+```dvc
+$ dvc gc -w
+```