Not sure I
quite understand the question, but I'll try to help.
You can open applications by typing
open -a "xxxx"; for instance,
open -a "App Store" will open the App Store if it's in the Applications folder. The '-a' modifier isn't necessary, but there are a lot of other options you can open an app with if you're interested.
If it's an app outside of the Applications folder, you can use
open -a FILEPATH. Filepath being, for example,
open -a Users/Username/Documents/App-You-Want-To-Open.app
If it's a file you just want to open, you can just say
open FILEPATH. So if it's a document,
open Users/Username/Documents/Document-You-Want-To-Open.docx
However there's a much easier way to open apps on startup. Just open the app as you normally would. You'll see it in the Dock at the bottom. Right-click that and select 'Options>Open at Login'. Then that app will always start as soon as you open the computer.
Could you outline exactly what you're trying to do (i.e., the scenario you need the fix for)? This might help us a little more.