How do I conjugate the past tense?

Regular verbs in Spanish follow a series of rules which are easy to follow and remember. Forming the past tense follows these rules - easy peasy!
You take the stem of the verb and add on certain endings, just as you would for the present tense.
[Quick recap: All spanish verbs in their basic form end in AR, ER and IR, most are regular some are irregular. When we say stem of the verb we mean the basic form of the verb without the AR, ER or IR ending. For e.g ROMPER = To Break. Stem of ROMPER = ROMP we then add on the endings to form tenses.]

Those past tense endings are as follows:

For AR verbs, such as TERMINAR (to finish) you add:

• É =Terminé (I finished)
  
• ASTE = Terminaste (you finished)
  
• Ó = Terminó (He/She finished)
  
• AMOS = Terminamos (We finished)
  
• ASTEIS = Terminasteis (You pl. finished)
  
• ARON = Terminaron (They finished)
  
  For IR and ER verbs  e.g. VIVIR (To live) you add:
  -Í = Viví (I lived)
  -ISTE = Viviste (You lived)
  
• Ó = Vivió (He/she lived)
  
• IMOS = Vivimos (We lived)
  
• ISTEIS = Vivisteis (You pl. lived)
  -IERON = Vivieron (They lived)
  
  And that's it! Now try and form some past tense sentences...