Yes. On the Conversation list, tap the contact letter/initial found on the left side of the conversation to start the multi-select process. Then, just tap any other conversations to select them. This allows you to delete, archive, and perform other actions on a batch of conversations instead of one at a time.
For individual messages, you can long-press one of them until a popup/dialog appears. After that, tap "Select Multiple Messages", then tap the other messages to multi-select them.