Short story is: you can't unless you're rich.
You can get tickets by registering on Wimbledons website. Then there is a public ballot where you can get the chance get the "opportunity" to buy random tickets for a random day (basically) they will assign a random dar/stadium and you'll choose if you want to buy the ticket or not.
The other option is to buy a permanent seat which can cost tens of thousands of pounds. (Whoever has these tickets can sell one day if they wish or can't go).