Ads are “rolling out gradually” to WhatsApp
The ads will appear under WhatsApp's Updates tab.

For the first time since launching in 2009, WhatsApp will now show users advertisements. The ads are “rolling out gradually,” the company said.
For now, the ads will only appear on WhatsApp's Updates tab, where users can update their status and access channels or groups targeting specific interests they may want to follow. In its announcement of the ads, parent company Meta claimed that placing ads under Updates means that the ads won’t “interrupt personal chats.”
Meta said that 1.5 billion people use the Updates tab daily. However, if you exclusively use WhatsApp for direct messages and personal group chats, you could avoid ever seeing ads.