"I wrote an application."
Translation:Jag skrev en ansökning.
Those are different things in Swedish, but since we don't know what is meant without context, several different answers are accepted. en ansökning is an application for a job or grant; 'a program' is ett program or sometimes en applikation, 'an application' in a more general sense ('the process of applying something' or 'the use of something') is en tillämpning (sometimes also used about computer programs).
Some verbs form past tense through a vowel change, just like in English (compare write -> wrote). Those verbs have to be memorized.
Here is a good list of strong and/or irregular verbs: https://en.wikibooks.org/wiki/Swedish/List_of_strong_and_irregular_verbs