"mangia, scrive" and "legge" are verb not adverb. "alta" is adjective. you're messing up
ad es: (io) mangio, (tu) mangi, (lui/lei) mangia... - I eat, you eat, he/she eats...
this is indifferent if the subject is male or female. 3° per sing of verb "mangiare" is "mangia" The adjectives instead are declined if singular or plural and/or if masculine or feminine
ad es: (io) sono alto(a) - i am tall.
(noi) siamo alti - we are tall
NB: There are three types of verb conjugation:
1st conjugation, indicates the verbs that infinitely end in -are (parlare, mangiare, pubblicare, etc.);
2nd conjugation, for those ending in -ere (scrivere, leggere etc.);
3rd conjugation, for those who end in -ire (dormire, sentire etc.).
Verbs that infinitely do not end in any of the three, fall into the second conjugation, (comporre, tradurre, etc.)
based on how they end in the infinite form they decline in a different way.
for ex: scrivere - to write: io scrivo, tu scrivi, lui/lei scrive, etc...
dormire - to sleep: io dormo, tu dormi, lui/lei dorme, etc...
parlare - to speak or talk: io parlo, tu parli, lui/lei parla...
I hope I explained and sorry for my bad English, but i am italian