Doctor Strange and other sorcerers in the MCU use a tool called a sling ring in order to be able to perform magic.
But why is a physical tool required to perform those mind-blowing magics? Isn't magic supposed to come from a soul?
They are only shown to require the sling ring to conjure the portals and travel from place to place. Other spells are performed regularly by people not wearing a sling ring.
There is a scene in Doctor Strange where Mordo gives the following explanation of magical relics.
This is a relic.
Some magic is too powerful to sustain, so we imbue objects with it allowing them to take the strain we cannot.
This is the staff of the Living Tribunal.
There are many relics. The Wand of Watoomb. The Vaulting Boots of Valtorr…
Notable in that scene is that Dr Strange then conjures a very similar effect to the staff of the Living Tribunal to spar with Mordo, but it takes him significant effort.
Sling rings aren’t mentioned here, but I think it is a reasonable assumption that the transportation spell would be too draining for an individual to actually do without a sling ring or some other external source of power.