That's a good question. It depends on the form the infinitive takes, whether it ends with
-ir. The infinitive of "to walk" is "caminar" and the infinitive of "to drink" is "beber".
Thank you so much sir for that chart , I honestly think that Duolingo should include the present tense chart in the (present tense) lesson ,instead of that useless endings chart they've put....some of us don't have a background on these type of languages so we don't always get it by instinct (Arabic native speaker)