Tap the Yahoo Mail app icon, which resembles a white envelope and the phrase "YAHOO!" on a dark-purple background. This purple Yahoo Mail icon is in the middle of the page. It's a link at the bottom of the screen. Doing so opens the account creation form. You'll need to type in the following information:  First name Last name Email address - Your preferred Yahoo email address. If your email address is already taken, you'll have to type in a different one. Password Mobile phone number - Without a mobile phone number, you can't create a Yahoo account. Birth date (month, day, and year) Gender (optional) It's the blue button at the bottom of the screen. If you've neglected to fill out any of the required fields or your selected username isn't available, you won't be able to proceed until you correct the problem. Doing so will prompt Yahoo to text a code to the mobile number you entered earlier. You can also tap Call me with an Account Key to have Yahoo call you and recite the code. Open your phone's Messages app, look for and open the message from Yahoo, and review the five-digit security code in the message. If you chose the Call option, wait for your phone to ring, then answer the call and listen to the recited number. This field is in the middle of the screen, just below the "Enter the Account Key we sent to [your number]" heading. It's the blue button near the middle of the screen. Doing so will take you to your Yahoo inbox, which is set up and ready for you to begin using it.

TL;DR in Indonesian:
Buka Yahoo Mail. Sentuh Yahoo Mail. Sentuh Sign up. Masukkan detail akun. Sentuh Continue. Sentuh Text me an Account Key. Dapatkan kode verifikasi. Tikkan kode pada kolom "Verify". Sentuh tombol Verify. Sentuh Let's get started.