Take them outside and stay with them until they toilet. Do this as soon as they wake from a nap, after meals, after playing with you, if anything exciting happens (someone at the door for example), and in any case at least every hour. When they toilet outside praise them lavishly. Don't expect miracles - however vigilant you are there will almost certainly be the odd accident. Don't tell your puppy off, as this can lead to them hiding from you to toilet indoors, but just clean it up using something like Simple Solution (something without ammonia). Puppies vary - I had one who was toilet trained very quickly (10 weeks), one middling (14 weeks) and one who took until 6 months. (This 'late developer' turned out to be a brilliant little dog, very engaged and quick to learn.)
As @Joy says, take out often, treat and praise. Use a word when he goes do you can use that as a command when older. Meg will have a wee now if asked. Ignore mistakes inside, and don’t expect total success until for quite some time yet. Don’t bother with puppy pads or newspaper, they just teach a dog it is ok to go inside. Meg was pretty much sorted at 14 weeks, but many take a while longer. Good luck.
