How to write by hand on Apple's mobile phone?

Long press the earth icon in the lower left corner of the keyboard and click "Simplified Handwriting".

Mobile phone software: iPhone 13, iOS 15.4.

Open a place where you need to enter text, such as a memo, and long press the earth icon in the lower left corner of the input keyboard. Among the options that Xiao Zu can open, click "Simplified Handwriting". You can call up the handwritten keyboard by talking casually. In the blank area of the bottom keyboard, you can write the words you need by hand.

Graffiti with "mark":

After choosing a marking tool (such as a pen, spring pen or pencil), choose a color and start doodling. Click the same tool again to change the color opacity; Or click another tool to change the thickness. You can also tap the Color button to change the chroma.

Where can I find screenshots?

Open photos, and then go to photo albums > media types > screen shots.