How do you form the imperfect tense?

Firstly, take a verb that you want to conjugate e.g. Comer (to eat). Take off the ending -er- leaving it as 'com' (do the same for -ar- and -ir- verbs) then add an ending using the imperfect tense verb endings. These verb endings differ depending on what the verb ends in e.g. AR, IR or ER. If we wanted to say 'we used to eat', we would take the verb 'comer', take off the ending -er-, then add the verb ending for 'we'. The 'we' form for an -er- verb in the imperfect tense is 'íamos', therefore making it 'comíamos'.This would be different for -ar- verbs for example 'comprar' (to buy). If we wanted to say 'I used to buy', we would take the -ar- off and add the imperfect tense verb ending to 'compr' in the 'I' form. The 'I' form in the imperfect tense for -ar- verbs is 'aba', making the verb 'compraba'. There are some irregular verbs in the imperfect tense which will be covered after the endings for regular verbs have been mastered.