A "Steps" table with parent_id
Mysql is not really my usual dbms, but looking at your sample I would suggest you another schema by adding [chapter], and use it like a hierarchyid field of MS Sql.

+----+----------+-------------+-----------+
| id | guide_id | description | chapter   |
+----+----------+-------------+-----------+
|  1 |        1 | Step 1      | /1        |
|  2 |        1 | Step 2      | /1/2      |
|  3 |        1 | Step 2.1    | /1/2/1    |
|  4 |        1 | Step 2.2    | /1/2/2    |
+----+----------+-------------+-----------+


Then indexing by guide_id + chapter you can fetch the whole tree, or you can get one chapter using:

WHERE chapter LIKE '/1/2%' ORDER BY chapter