Learn Italian: Potresti mandare il link nel gruppo, per favore? - Could you send the link in the group, please?

Potresti is the conditional form of potere (can/to be able to), meaning 'could you'. Just like in English, using 'could you' is a more polite and softer way to ask for a favor than saying 'can you' (puoi).

I thought 'to send' is inviare. Can I use that instead of mandare?

Yes, absolutely! Mandare and inviare both mean 'to send' and are interchangeable here. Mandare is slightly more common in everyday spoken Italian, while inviare is a bit more formal, but both work perfectly for sending a link or a message.

How do we know to use il for the English word link?

In Italian, foreign loanwords are almost always treated as masculine by default. So, 'the link' becomes il link. As a bonus rule, foreign words ending in a consonant do not change their ending in the plural, so 'the links' would simply be i link.

Why is it nel gruppo (in the group) and not al gruppo (to the group)?

When talking about messaging apps, Italians usually talk about sending things 'inside' the chat or group. You combine the preposition in with the masculine article il to get nel. While al gruppo isn't strictly wrong, nel gruppo is the most natural way to say you are posting something in a group chat.