When the water pressure at a faucet is fine one day but lower the next day, there may be a piece of debris blocking the opening. Remove the handle and bonnet nut, then unthread the stem and check the washer. If the washer looks fine, turn on the water and flush out the spigot. If you have good water pressure you've solved your problem. If not, reassemble everything, then repeat the procedure at the inside valve. If neither of these solves the problem with your garden faucet, then you probably need to call in a plumber to run some more detailed diagnostics.
If there is no water at the faucet, then the problem might be the aerator or inside the faucet spout. Debris can get into the strainer at the end of the faucet spout. This is a device that screws into the end of the faucet spout to restrict the flow of water and add air to the water so the water will not splash when it hits the sink. The flow restrictor is in the back end of the aerator which is in the faucet spout opening. Unthread the aerator from the spout and clean it out. If this isn't the problem, then remove the spout and check for debris.