When you first start the Campaign in Sniper Elite 4, you start the first mission, San Celini, in a tutorial which will guide you through the basic controls with on-screen prompts.
Your controls will be limited until you've completed this section, which gradually increases what you can do.
The first step is to climb the pole up to the ledge where there is a soldier standing guard. When close enough you will get a prompt to perform a Melee Kill.
After that, and once you have climbed onto the ledge, you will be prompted to use your binoculars to tag the crane and the two enemies. The prompts will tell you which buttons to use.
Shoot the crane to drop the cannon on the two soldiers. Next follow the objective markers to clamber up to the start of the level. There will be one last prompt to open your map screen, and then you'll be let loose to sneak around to your heart's content!
On subsequent playthroughs of this mission you will get the option to turn this tutorial mode off: