Sending messages to androids

Do you also have an iPhone?

If yes, use Continuity, read here => How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

FYI, SMS piggyback on the voice line, which iPad do not have (iPad is not a phone).

The only way to send SMS is via an associated iPhone.

As long as you own an iPhone, you can use Continuity Services to send text messages by using Text Message Forwarding. If you do not own iPhone, you cannot text with anyone other than other iOS based users via iMessage.

See this link about Continuity Services and click on Text Message Forwarding --> Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

If you don’t have an iPhone to pair with the iPad, you and your Android contacts will have to use a common internet messaging service, like Google Hangouts, Skype, WhatsApp (WhatsApp requires a cellular telephone to make an account, but with an account, an iPad can use WhatsApp Web) or some such cross platform internet messaging service.