Telegram allows you to format text inside your messages. Highlight a word or paragraph and select in the formatting menu (right click on the highlighted part in the desktop clients) your formatting. If you need bold and italic at the same time, you could use Telegram's Blogging platform Telegra.ph, but make sure to connect the page to your account via the @telegraph bot.
To bold your message, place two asterisks on both sides of the text: **bold**
To italicize your message, place two underscore on both sides of the text: __underscore__
To unterscore your message, place <<UNKNOWN>> on both sides of the text:
To strikethrough your message, place two tilde on both sides of the text: ~~strikethrough~~
To monospace your message, place three backticks on both sides of the text: ```text```