To make the handlebars more comfortable, you can cover them with specially made slightly padded tape or put grips on them depending on which type of bar you are using
The drop handlebars on road bikes are best suited to taping as there is quite a long length of the bar which can be used. Tape is manufactured in a variety of materials from cloth, to cork and also available with gel inserts to increase padding. Tape is supplied in two rolls per pack with one roll covering each side of the handlebar. A small sticky section on one side helps keep the tape from slipping off the handlebars and a small amount of insulating tape is usually applied at the end of the tape near the stem to prevent the handlebar tape unravelling.
Flat handlebars are better suited to grips as there is a much smaller space for the hand to grip at each end of the bar. Grips are thicker than tape and so provide more protection from shocks coming up from the front end of the bike. They are mostly made from rubber, although also available in cork and leather amongst other materials, with varying thickness depending on hand width and rider preference. They are slid over the open end of the bar with a bar end cap to cover the open end. New grips often come with locking ends which are kept in place with a small grub screw to stop the grips from moving round the bar.
Good way to stop grips moving round the bar - apply hairspray between the bar and grip when putting them on., trust us it works! Good way to help take them off - spray some water displacing fluid between the grip and the bar.