Muting a conversation will prevent it from generating notifications. To mute a conversation, access it, then tap the 3-dot menu on the top right. After that, select the Conversation settings or Group settings, and flip the toggle labeled Mute Conversation.
You can also long-press and select as many conversations as you want from the Conversation list, then tap the 3-dot menu on the top right and select Mute/Unmute Conversation.