Client Web apps

How would you integrate a application into a webflow?
I’m relatively new to webflow and have 0 knowledge in code. So excuse any mistranslations or unbased knowledge.
How easy is it to integrate a application into webflow. Say I’m outreaching a client and they have a site that after logging in allows you to use their software or app service. But i need to build in webflow and transfer the apps functionality

what is normal protocol?
Is it hard to achieve this?
what steps are taken to do so?
is there a lot of code required?
or is it as easy as copying a embed code or api key into an embed element?
Would the client know what is needed to for me embed the code into a website (ie a string of code, or API access link? if that’s a thing :question::sweat_smile:
Do you just link to another domain?

could anyone point me in the direction of video’s, articles etc that would help me.
thank you