"Podía" is the imperfect (pretérito imperfecto) of verb "poder"of indicative mode: "yo podía hacer eso, ahora no". "Podría" is the conditional (modo condicional) of the same verb of indicative mode: "yo podría hacerlo si tú me ayudas".

Hi!! 1) " Podía": it is the same as "I used to". Example: I used to sing very well (Yo podía cantar muy bien) 2)"Podría": i think this word indicates a possibility, it is similar to " may/might/could". Example: If i drink a lot of beer i could lose control and dance on the table (Si bebo mucha cerveza podría perder el control y bailar encima de la mesa) Im a spanish speaker but not a Spanish teacher, only used my common sense, i hope it´ll be useful for you.

They both translate as could in English but as Albert says podia in the past and podría in the conditional. Podia could also translate as "was able to". These examples may help: I couldn't finish my homework. - No podía terminar los deberes. If I had more time I could do my homework better. - Si tuviera mas tiempo, podría hacer los deberes mejor.