HTML has special handling for characters like < and > symbols, so it doesn't work well with those characters where they shouldn't be.
Having spurious characters like those symbols in your text can have some weird effects - blocks of text not appearing, broken formatting, and generally just not seeing what you expect to see.
This can all be fixed by 'escaping' those characters. This process involves scanning the text for those characters, and replacing them with a special character-code that browsers can interpret as the correct symbol, without actually embedding that symbol in your text.
Paste your Adsense code or any HTML in the empty box and then press the Convert button