I would suggest using a Raspberry Pi servo hat if you're just starting out and want to learn how to use servos.
There are a lot of them on the market but I'd go with something from Adafruit as they have a lot of very nice tutorials to go along with their products.
https://www.adafruit.com/product/2327
On that page they also link to an article on external power supply's to be used with the hat.
https://learn.adafruit.com/adafruit-16-channel-pwm-servo-hat-for-raspberry-pi/powering-servos
EDIT:
To connect a servo via a breadboard and an external power supply you can have a look at this video: https://www.youtube.com/watch?v=LwEBB6v559I
Adafruit also has a tutorial on this: https://learn.adafruit.com/adafruits-raspberry-pi-lesson-8-using-a-servo-motor
Both uses batteries (I know you don't want to use batteries) but it will show you how to connect things. You can always swop out the battery pack for a power supply.
As for a power supply that you can use, Adafruit recommends this for up to 4 servos: https://www.adafruit.com/product/276
The specification that you're looking for is 5V 2A.
Perhaps these Amazon links will help:
https://www.amazon.com/Universal-Adapter-5V-Power-Connector/dp/B0789PJR62/ref=sr_1_10?crid=X9QWFDLSR1I8&dchild=1&keywords=5v+2a+5.5mm&qid=1614816805&sprefix=5v+2a+5.5%2Caps%2C386&sr=8-10
https://www.amazon.com/DAYKIT-Female-2-1x5-5MM-Adapter-Connector/dp/B01J1WZENK/ref=sr_1_5?crid=Y62EQWCBQA9P&dchild=1&keywords=5.5mm+barrel+connector&qid=1614816875&sprefix=5.5mm+bar%2Caps%2C387&sr=8-5