You can achive this in different ways. I think the best way for you will be next:
Add additional field to your content type Properties
-> for example featured
interger value. Next you will need to install Views module, this module is really strong and awesome, you can display any content you want in block or any aother way.
Then go to Structure
-> Views
-> Add new view
, and create new view, chose Create a block
instead of creating page, set title and description, Display format
- chose what you need or prefer( i suggest to use unformatted list) of fields
- > Save and continue.
Next you will need to add FIELDS
you want to display, click add
and chose -> Content: Image
and Content: Title
there are different settings for this fields(uncheck Create a label). Next click on ADVANCED
and click add a Contextual filter
and chose your field you have created for your node - Content: featured
(or any other name you have chosen when created your field in node). Click on it and in WHEN THE FILTER VALUE IS NOT AVAILABLE
- and in Provide default value
chose fixed value
and set it 1,2,3
comma separated.
Save and your view is done, now go to Structure
-> blocks
and add your view to your region you need.
In your nodes which you want to display in field featured
add 1
to - display first 2
second, 3
to display third. Now you can manage what nodes to display as featured.
Oh i forgot, in your view SORT CRITERIA
- chose Content: featured
.
Also you can do this with Flag module, but i don't have much time right now to explain.
Good luck.