Learn Croatian: Ja sudjelujem u akciji. - I participate in the campaign.

Verbs that end in -ovati or -ivati change their shape in the present tense. They drop the -ova- or -iva- part and replace it with -uje- before adding the standard endings. So, sudjelovati drops -ova-, adds -uje-, and takes the "I" ending -m to become sudjelujem.

Why does the word for campaign, akcija, end with an -i here?

It is in the locative case. The preposition u (in) triggers the locative case when you are talking about being somewhere or taking part in an event, rather than moving toward it. For feminine words ending in -a like akcija, the -a changes to an -i.

Does akcija just mean "action"?

It does translate to "action", but in everyday Croatian, it is most often used to mean a "campaign" (like a charity drive, environmental cleanup, or political campaign). It is also the word for a "special sale" in a store. If you see a store window saying akcija, it means items are discounted!

Can I drop the word ja and just say Sudjelujem u akciji?