Laser print is an OUTPUT device - it takes output from computer and prints it.
Mouse is an INPUT device. It supplies input to computer about coordinates x,y.
Hard drive is a secondary memory storage device. It stores data in files, permanently. So CPU can retrive the data by reading from hard disk drive and load it into primary memory and then perform operations/commands on that data and later store it back on to the drive.
CPU is the main part of computer - processing unit. It performs commands / mathematical & logical operations on data/values. it has registers and access to primary memory ie., ROM & RAM. CPU performs operations directly on data in registers and can load & restore data from to RAM & ROM.
RAM : random access memory: when power is off, all data is lost in it. CPU can load some data into the RAM and can perform calculations on that data. CPU can restore that data from RAM onto hard disk or DVD or CD or it print that data by sending it to an OUTPUT device.
ROM : read only memory. thedata in this is not erased when power is off. It stores important instructions for the computer (CPU) to do when power is switched on. So the computer boots and starts with instructions stored there.