one way to understand the ot is from the jewish perspective. the jews divided their scriptures (which is similar to our ot) into 3 sections called Torah, Prophets and Writings. Under the first section, Torah, there are 5 books - Genesis, Exodus, Leviticus, Numbers and Deuteronomy.
The second section, Prophets, has two sub-parts - Historical books (consisting of Joshua, Judges, Samuel and Kings) and Prophetic Books (consisting of Isaiah, Jeremiah, Ezekiel and the Twelve Minor Prophets). Note the Jewish way of counting is different from the Christian. Samuel and Kings were originally only 2 books (we have split them further to make 1 and 2 Samuel and 1 and 2 Kings). Also the Twelve Minor Prophets were counted as one book (since they were written in a single large scroll).
The third section, Writings, consists of the rest of the ot books - Psalms, Job, Proverbs, the 5 Scrolls (Song of Songs, Esther, Lamentations, Ecclesiastes and Esther), Daniel, Ezra-Nehemiah and Chronicles. Note again, Chronicles was originally 1 book and so was Ezra and Nehemiah. That makes 24 books in all in the Jewish scriptures cf. with the Christian counting of 39 books.