Can an iPhone make a call to a Samsung?

sure, it can call all phones also old landlines and old nokia 3310 

Why not, what happens when you try

I have this problem with a Samsung galaxy. When I call the Samsung it rings then I get a message that “your call has been forwarded to an automatic voicemail system”. Text messages are sent but never received by friends Samsung

I need to call my friends and cant

That's an issue on their end, not yours.