ARE & ERE share the same verb endings:
io - erei noi - eremmo
tu - eresti voi - ereste
lui/lei - erebbe loro - erebbero

IRE verb endings:
io - irei noi - iremmo
tu - iresti voi - ireste
lui/lei - irebbe loro - irebbero

Conjugate MANGIARE, a regular ARE verb in the conditional tense:

io mangerei - I would eat
tu mangeresti - you would eat
lui/lei mangerebbe - he/she would eat
noi mangeremmo - we would eat
voi mangereste - you all would eat
loro mangerebbero - they would eat

Although Mangiare is a Regular ARE verb, you do eliminate the I after the G when conjugating it, this happens in some other verb tenses also, such as the Future Tense.

COULD. We use POTERE as the helping verb, its an irregular verb, and we conjugate it in the conditional tense. Here are the verb endings for POTERE and also DOVERE:

io - rei noi - remmo
tu - resti voi - reste
lui/lei - rebbe loro - rebbero

Potere:

io potrei - I could
tu potresti - you could
lui/lei potrebbe - he/she could
noi potremmo - we could
voi potreste - you all could
loro potrebbero - they could

Here's how you say COULD EAT:
io potrei mangiare - I could eat
tu potresti mangiare - you could eat
lui/lei potrebbe mangiare - he/she could eat
noi potremmo mangiare - we could eat
voi potreste mangiare - you all could eat
loro potrebbero mangiare - they could eat

To say SHOULD, you conjugate DOVERE in the Conditional Tense, in a similar way to POTERE:

io dovrei - I should
tu dovresti - you should
lui/lei dovrebbe - he/she should
noi dovremmo - we should
voi dovreste - you all should
loro dovrebbero - they should

Here's how you say SHOULD EAT:

io dovrei mangiare - I should eat
tu dovresti mangiare - you should eat
lui/lei dovrebbe mangiare - he/she should eat
noi dovremmo mangiare - we should eat
voi dovreste mangiare - you all should eat
loro dovrebbero mangiare - they should eat

Here's how you conjugate a Regular IRE verb (Dormire - to sleep) in the conditional tense. The verb endings are show above, but they're very similar to the ARE and ERE verb endings:

io dormirei - I would sleep
tu dormiresti - you would sleep
lui/lei dormirebbe - he/she would sleep
noi dormiremmo - we would sleep
voi dormireste - you all would sleep
loro dormirebbero - they would sleep

Here's how you conjugate a REGULAR ERE (LEGGERE - to read) verb in Italian, it follows the same verb endings as I showed above for ARE verbs:
io leggerei - I would read
tu leggeresti - you would read
lui/lei leggerebbe - he/she would read
noi leggeremmo - we would read
voi leggereste - you all would read
loro leggerebbero - they would read