Sometime you have seen the formatted messages of WhatsApp. We can only format the text messages in which we can make text bold, italic, strikethrough and monospace so following is the syntax to me the text formatted.
Bold: Use asterisk on both side (*bold*).
Strikethrough: Use tilde on both side (~strikethrough~).
Italicize: Use underscore on both side (_italic_).
Monospace: Use three back ticks on both side (“`monospace“`).