Aftermarket radio installation?

[Zac]

I don’t know what I need to install an aftermarket radio. I need to find the wiring harnesses and faceplate to match. Also the amplifier thing to stop speakers not getting power. I think this is right but not sure ha ha. Any help appreciated. Im new to cars. It’s a 2007 Audi A3.

[Steve Q]

This video should help: 

And here's an example of what you need: 

https://www.halfords.com/technology/car-audio/stereo-fittings/audi-installation-kit-ctkau01-577715.html?istCompanyId=b8708c57-7a02-4cf6-b2c0-dc36b54a327e&istFeedId=367c5610-f937-4c81-8609-f84582324cd6&istItemId=wirxtppmt&istBid=t&_$ja=tsid:|cid:16710940973|agid:|tid:|crid:|nw:x|rnd:5504221901323466582|dvc:m|adp:|mt:|loc:1006867&gclid=Cj0KCQjwpv2TBhDoARIsALBnVnnhiVPfUOld-jAQbCCwdHmYtec2tlp7b7_fnyREVO_7paGhFpdQ-yYaAn7_EALw_wcB