1) Press and hold an email you wish to select.
2) Press the picture/letter icon of every additional mail you want to select.
3a) For Imap: Press the icon representing three vertical dots on the top right corner of your screen and select "Move".
3b) For Exchange: Press the "Move" button on the top edge of the screen (the one that looks like a folder)
4) Choose the folder you wish to move them to.