Hi. I learned some sounds (also తొమ్మిది) from Magadheera movie. This film begins with count from 1 to 100 (some numbers) and it was very helpful for me. It's free on YouTube.

The symbol after మి is the ma-ottu. It is the secondary form of మ. In Telugu, we write in syllables. First we write a primary letter (అక్షరం / aksharam), then we write the secondary vowel (గుణింతం / gunintam), then we write the secondary consonant (ఒట్టు /ottu). But, the reading order is different, the secondary consonant sound comes before the secondary vowel. You can think of secondary consonants as similar to when we have two consonants in English. For example, in the word "summer". Imagine that we write the 2nd "m" under the first one, but write it a little smaller to save space on the page & to draw more focus to the first "m".

Hi! Turns out it just adds another 'm' sound (tomMidi)

Hı How are you