"However" is a transitional word that moves your ideas from one sentence to another. It's very similar to "but." It's used to show contrasts and differences.
Having a car can be very convenient; however, it's expensive to buy and maintain one.
Walter has a lot of work to do; however, he's too tired to finish it.
Jim is in love with Graciella; however, he's not sure if she loves him.
However hard she tried, she could not open the door to get the office supplies.
However = No matter how
Bill doesn't mind working late; however, he's a little scared of walking home by himself at this time of the night.
Beekeeping is an important occupation; however, the beekeeper must keep himself covered at all times.