Take a look at the above chart? We´ll take the example of, ´I am sick´, can you notice in turkish you write it as hastayım. The ´y´ is what you call a buffer letter and in turkish you use the buffer letter when you have to separate two vowels. For example if we didn´t use the buffer letter then ´I am sick´ would be spelt as, ´hastaım´ - can you see the 2 vowels ´a´ and ´ı´ would be together. In turkish you can´t have 2 vowels together so that´s where the buffer letter ´y´ comes in to separate them hence the correct way to spell, ´I am sick´ is ´hastayım´.

Let´s do a few more examples:

Take a look at both of the charts now: can you see that when you say, ´he is sick´ or ´he is alone´ the spelling is, ´o hasta´ or ´o yalnız´. In turkish he/she/it doesn´t have a personal ending. 

if the verb ends in ´e´ then the suffix will start with either (y)im /sin /(y)iz /siniz /ler

if the verb ends in ´a´ then the suffix will start with either (y)ın /sın /(y)ız /sınız /lar

if the verb ends in ´u´ then the suffix will start with either (y)un /sun /(y)uz /sunuz /lar

if the verb ends in ´ü´ then the suffix will start with either (y)ün /sün /(y)üz /sünüz /ler