Start in the Photos app. View the album or section where the photos you want to email are. Make sure you are using the grid / thumbnail view (with many photos visible at once). This is where you select multiple photos.
Press the Arrow toolbar button on the top right of the screen.
This will allow you to select individual photos. Tap on each one you want to email and they will get a blue tick against them.
When all the photos you want to email are selected, press the "Share" button on the top left, and then choose email.
A new email will be created with all your photos attached!