Email Is Like An ID Card And A Password Is Your Face
Its A Way To Differentiate Every Account That Exist In Their Database A Username Can Do That Too But Thats Not The Point
This Can Be Your Secondary Email For Other Things You Want To Be Very Secure
There Is A Lot Of Email Providers But The Most Popular Is Proton Mail Because It's Free But If You Have A Bit Of Money You Could Use Tutanota
While Having Another Email Is Great But Realistically We're Just Lazy To Check 2 Emails So We Use An Alternative Which Is Email Aliasing Basically they Gave You An Email That You Can Use Anywhere And Any Mail That The Email Receive It Forwards It Tu Your Real Email And You Can Disable Or Even Delete The Email If You Login In A Scam Or Spam Website
Email Aliasing Services That Is Good ( And Free ) Is AnonAddy And Simple Login
Both Are Great And Really Simple To Use ( But AnonAddy Has Unlimited Standard Aliases But I Haven't Tried It Yet Will Update If I Ever Try It )
2FA Is Great Always Enable It In Every Website It Supports It Including Email Or Email Aliasing Services In 2FA I Talk About 2FA In More Detail