When it comes to self, yo goes with verbs end with o. For example yo bebo, yo hablo, yo como… What is the reason for this grammar structure? Was it because the o sound at the end of yo that makes the original Spanish speaker thought of such derivation? For the other person tu goes with verb that ends with s, for example tu comes, tu bebes. On the other hand, el and ella go with verbs that does not have s. For example, el bebe, ella habla, el lee.
There are no is/are. The subject and the verb or position indicator.