Basically when talking in the “yo” form, end the word with an “o”. When talking in the “tu” form end with an “es” or “s”.
When taking in the “Ello,Ella,or Usted form” end with an “e” or “a”. When talking in the Ellos,ellas,or ustedes form end with a “an”. And last but not least when taking in the nosotros form, end the word with “mos”. This can be used for your current situation but might not be so reliable in future Spanish assignments.