You shall first have to connect your Sinclair ZX Spectrum, Amstrad CPC, Commodore Amiga or Commodore CDTV (and cassette recorder, in the cases of the 8-bit versions) to your television, then switch all three (or both, in the cases of the Amiga and CDTV versions) of them on; in the cases of the 8-bit versions, you shall now have to place the cassette of The Edge's Consult Software-developed 1989 adventure game Snoopy into the cassette recorder, rewind it (unless this is your first time playing it), start it, type LOAD "" (without leaving a space between the quotation marks) and press to load the program into the console (however, for the cases of the Softek International-developed Amiga and CDTV versions, you will have to insert the disk or CD into the console's appropriate drive, and the program will be loaded automatically). At this point in the 8-bit versions, the text "STOP TAPE" will then appear on the screen - and, once you have done this, you shall have to press to select keyboard control, to select Kempston joystick control if connected or to select Sinclair joystick control if connected (in the CPC version, option 2 will not be present, so option 3 will be option 2). Once you have made your selection, the game will start (in the 16-bit versions, no options are present on the title screens on the pretext they only support joystick control, so you will just have to press the button on the joystick to start the game); a solution for it was published in Your Sinclair magazine in May 1990.
You'll first have to make Snoopy walk up to his bowl of dog food, eat its contents and put it down, then walk to the right behind the kennel (he'll reappear holding a typewriter), put it down and type something on it, walk back behind the kennel (he'll reappear holding the note he has typed), continue walking to the right, give the note to Charlie Brown, pick up the sweet jar then eat its contents, continue walking to the right up to (and to the ninth screen of) the third row, put the jar over the frog to make a barrel start rising out of the water, put the frog-filled jar down, retrace your steps back to the left, pick up the football, retrace your steps back to the ninth screen of the row, jump onto the barrel and a mooring post in turn, kick the ball into the water (it shall float), retrace your steps back to the left again (the aforementioned Charlie Brown shall be on the sixth screen of the row with his note this time, and Schroder shall be on that fifth one), pick up the catapult, retrace your steps back to the right again (both Schroder and Charlie Brown shall be on that sixth screen this time, the latter without his note), jump onto that barrel and mooring post in turn again, jump onto that ball and two more barrels in turn, fire a rock at the balloon that is emerging from the well to burst it (it has a bicycle pump tied to its string), pick up the bicycle pump, retrace your steps back to the left once again (Charlie Brown will be on that fourth screen this time), drop the bicycle pump on the first screen of the row (the Baseball Field), retrace your steps back to the right once again, go up the path to the Van Pattens' house (second row), continue walking to the right (both Schroder and Linus shall be on the second screen, and the latter will say SNOOPY I'VE LOST MY BLANKET), take the deflated swim ring from Lucy, retrace your steps back to the left down to that first screen of the third row (Charlie Brown will be on that second screen this time), drop the deflated swim ring, pick up the bicycle pump, use it to inflate that swimring and put it down, walk to the left, pick up the brick, retrace your steps back to the right yet again, throw it into the air (Snoopy will say THIS IS A BRICK) to hit the apple in the tree, and make it fall to the ground, pick up the apple, continue walking to the right, go up the path to the school (first row), continue walking to the right (Peppermint Patty shall be sleeping on the third screen), put it on the desk to make a whistle appear on the ground, retrace your steps back to the left, blow the whistle to wake Peppermint Patty (she will say YES MA'AM I'M AWAKE, and drop a pair of scissors), drop that whistle, pick up the scissors, continue walking back to the left, go back up the path to Charlie Brown's house (the fourth row, and there will be a styling head there now), use the scissors to cut the hair of the styling head, drop the scissors, walk back to the right onto, and to the sixth screen of, the third row (Linus will be on that screen this time), go up the path to the Van Pattens' house again, give that styling head to Schroder, walk up to Lucy (to make her disappear), retrace your steps back to the left, pick up the blanket (which has come out of that now-open dryer), continue walking back to the left (Lucy will reappear upon the second screen) onto the sixth screen of the third row and give the blanket to Linus. At this point in the 8-bit versions, the text START TAPE shall then appear on the screen - and once you have done so, the text of CONGRATULATIONS. YOU HAVE COMPLETED THE JOE COOL COMPUTER GAME. shall appear on the screen ("Joe Cool" was a pseudonym Snoopy went by when he was being a private detective for the strip, and for the 16-bit versions, the ending text shall appear on the screen automatically when you give the blanket to Linus).