Go back to the infinitive, go back to the infinitive, go back to the infinitive. Don't just drop off an "o" or an "a." You have to go back to the infinitive & drop off an -ar, -er, or -ir.
The blue table is a summary of verbs that spell change. "V" stands for "vowel," so "ViV" is an "i" between two vowels.
The pink table is a summary of -ir stem-changing verbs. e --> i & e --> ie verbs get an i in the third person; o --> ue verbs get a u in the third person.
The yellow table is a list of irregular verb stems. You need to memorize the irregular verb ENDINGS (-e, -iste, -o, -imos, -isteis, -(i)eron).
The background color of the words is a hint. If a word has a blue background, you can look at the blue box to see what's going to happen; if it has a pink background, you can look at the pink box. Somtimes you'll see a verb that's highlighted one time & not the next. That's because PERSON is important when deciding whether the verb will change.
The tables are meant to be REMINDERS, not full-fledged explanations. If they don't make sense to you, you need to review before doing the exercise.