Ir, ser, and tener are great examples for irregular/stem-changing verbs in Spanish. Ir and ser have no -ar, -er, or -ir ending, so their conjugations are different. You just have to memorize them.
Tener in the past tense is strange. It changes much more frequently according to which pronouns you are conjugating it to. It's something like tuve, tuviste--sort of like ir and ser's past tense: fui, fuiste.
All-in-all, irregular verbs have no rules. Memorizing them is the only way to know them.
I think you confusing terms we are in preterite estuve for instance is the preterite for estoy. I just put a verb and asked for conjugations of root or even ar verbs ir verbs in search will bring up multiple sites in which to find all the verb tenses and conjugations its AMAZING how many ways to use one verb !!!!
Question: in the tips and hints it gives general info about the Preterit /past tense. Yet, estar is irregular in the past tense. Does Duolingo expect you to already know this or when a word appears that you don't know at all, are you suppose to 1 get it wrong or 2 look it up before replying?
I am having a hard time understanding something. It seems to me like sometimes -o, and other times -e indicates first person past tense. Is there a general rule? I would think this sentence would read "Ayer yo estuvo en el restaurante." Could somebody help explain why I'm mistaken? Thank you!!!
Just a general comment. I think this is really the first section on past tense and, at least to me, a relative beginner, it is a very confusing mix of all kinds of past tenses. Very messy and very unlike the earlier material that I found systematic and much easier to get. Duolingo, I think you can do better in this area. Great tool otherwise!