Two of the most frequently confused Spanish verbs are ser and estar, both meaning 'to be.' Ser expresses identity, essence, and permanent characteristics such as nationality, profession, time, and possession. Estar expresses state, location, mood, weather, and temporary conditions. So 'I am tired' uses estar because tiredness is a temporary state: estoy cansado or estoy cansada. 'She is a doctor' uses ser because profession is part of identity: ella es médica. The guiding rule is that ser describes what something is by nature, while estar describes how or where something is right now.
The verb gustar (literally 'to please') uses an unusual construction in Spanish. Rather than saying 'I like coffee,' one says 'Coffee is pleasing to me': Me gusta el café when the subject is singular, and Me gustan las manzanas when the subject is plural. The verb agrees with what is liked, not with the liker. To express 'there is' or 'there are,' Spanish uses a single form: hay. Hay un libro means 'there is a book,' while hay libros means 'there are books.' This impersonal form derives from haber and never changes for number.
Several verbs have special yo forms that learners should recognize. The verb caer (to fall) becomes yo caigo, following the same g-stem pattern as tengo (tener), pongo (poner), salgo (salir), hago (hacer), traigo (traer), and valgo (valer). Similarly, verbs like conocer, conducir, ofrecer, and traducir add -zco to the yo form: conozco, conduzco, ofrezco, traduzco. Finally, formal speech uses usted instead of tú, and usted takes the third-person singular ending rather than the second-person, so 'you (formal) speak' becomes usted habla, not tú habla.