This letter stands thirty fifth and writes the sequence of a glide followed by the vowel e. It carries no numeral value.
Like the iotified a it is a ligature, formed from the glide sign and the letter yest, and its two parts remain visible in the letterform. Old Church Slavonic distinguished the sequence it writes from the plain vowel e, and the distinction is real and grammatically loaded: it appears at the beginning of words and after other vowels, where the plain letter appears after consonants.
The distinction did not survive in the East Slavic tradition. The two letters fell together, and Russian ended with a single letter doing both jobs, its reading determined by position: at the start of a word or after a vowel it carries the glide, and after a consonant it does not, marking the consonant as soft instead. That is the same reinterpretation that overtook every letter in the iotified series.
Other Slavic languages went differently. Ukrainian keeps two separate letters for the plain vowel and for the glide plus vowel, so the distinction Old Church Slavonic made is still written there, with different shapes and by a different route.
The letter itself is gone from every modern alphabet, and it is one of the clearest cases in which what disappeared was a spelling rather than a sound.