Open File Action
This action opens the file or files Alfred feeds to it. Connect a Trigger (e.g. hotkey) or an input (e.g. file filter or keyword) to it.
Optionally, you can drag an application to the Open File action to tell Alfred to open the file in a particular application.
Using a File Filter with Open File
Use a File Filter input and drag in specific file types you want to open, e.g. images only. Connect your File Filter to the Open File action, and drag Safari in to open your images with Safari when using this workflow.
Specifying a file
Instead of dynamically opening the file fed through by a file filter, you can also choose a specific file you want to open with Open File. To do this, double-click the Open File object and drag your file into the left box.
Create your own workflow
You'll find a template for this type of workflow (and many more) built into Alfred.
In the Workflows preferences, click the [+] at the bottom of the sidebar > Templates > Files and Apps > File Filter from hotkey and open.