Hello Carolina, It is the difference between Past and Present. When you use 'I do' something you often refer to a habit in the present time as in : " I do my job everyday." If you refer to a present action, that is being done momentary, you rather use the 'present continuous tense' as in: " I am doing my homework NOW." You use 'do' in the present as well to emphasize and confirm the action of another verb as in : " I do like you." It is an emphasize on liking someone here. " I did my homework yesterday." 'did' is used exclusively to refer to actions that terminated in the past

Hi this Italki grammar site will help you http://www.italki.com/knowledge/contribution-ENGLISH+GRAMMAR.htm

Exactamente... I do - eu faço I did - eu fiz (Na verdade, o verbo "fazer" pode ser "to do" ou "to make" em ingles e isso depende na situaçao). Presente simples (Eu) I do (Voce/Voces) You do (Ele/ela/coisas) He/She/It doES (nós) we do (eles/elas) they do Passado simples I did you did he/she/it did we did they did

I did = past I do = present

the difference is that did you write for prayers in the past and do you write for this..