... can my camera trigger this external flash?
Yes, but not as a Canon wireless master. You have to put the YN-560IV into S1/S2 optical slave mode (use the Lightning/Radio button), and use the pop-up flash as a regular flash. You use S1 if the pop-up flash is in M mode; S2 if it's in TTL, so you can skip the metering pre-flash.
Keep in mind the S1/S2 "dumb" optical slaving is completely different from the Canon optical wireless system.
Does the popup flash in my camera always has to stay up to trigger the external flash?
Yes. Something on the camera has to tell the flash when to fire. And that's either going to be the pop-up flash, or a radio transmitter. Without the add-on transmitter, you have to use the pop-up flash, and it has to fire a pulse bright enough for the slave sensor to "see". You can set the power of the pop-up to be minimal, and it should not register in the image at regular (non-macro) subject distances.
If this is possible, will there be any difference using a build in trigger vs an external one?
Yes. If you get a YN-560-TX transmitter, you won't have to wrestle with the line-of-sight issues required by optical slaving. The light sensor on the flash has to be able to "see" your pop-up flash to be remotely triggered, so it's difficult to use a flash behind you, or behind a solid object. The light signal can also be overpowered if you try to use optical slaving outside in bright sunlight.
The YN-560-TX is a radio trigger, so isn't affected by either of these factors. In addition, it can let you remotely set the power and zoom on the flash from the camera.
However. A Godox TT600 and X1T-C combination would cost roughly the same and also give you HSS capability over the remote flash, while giving you far better expansion options in the future.
I will be using a soft dome or a reflecting umbrella sometimes so will they be in line of sight using the internal trigger?
Depends on how you set things up and whether there are bounce surfaces around. The red panel on the front of the flash is where the optical slave sensor is.