In this lesson you are going to learn how to read and write た、ち、つ、て、と. Adding two small lines called 濁点dakuten, but commonly known simply as 点々tenten, meaning "two marks", causes clear sounds to change to their voiced sound. Thus, adding the 点々tenten marks to た、ち、つ、て、and と will produce だ、ぢ、づ、で、ど.
By adding a small "っ" (tsu) in front of a syllable, it causes the subsequent consonant to double. This is called the sokuon (促音). This kana results in a slight pause between the two consonants (a double consonant pause). There is an exception for the kana ち. Instead of having a 'cch', a ~tch is used.
A couple examples are かった (katta) and しっけ (shikke).