If you know the name of the campaign you're looking for, go to the Home screen and tap on the "Campaigns" tab. 

On the header look for the magnifying glass icon to open the search bar. Enter the campaign name and tap on search on your keyboard. Any campaigns with that name will be shown below. 

If you're not sure what the Campaign is called, you can use the filter tool to narrow down the results. On the "Campaigns" tab, tap on the filter icon in the top right corner. From there, you can filter campaigns by category, location or organisation. You can also search for closed campaigns in case you are looking for past projects. 

Tap "Apply filter" to see your results.