The Dota Major Championships were announced back in April, but details were sparse. Now that the "fall" event is closer, we've got more information, specifically that the first Major will take place in Europe in November. There'll be another tournament in winter and spring, and then the International next summer.
If you want to attend, you'll have to wait for further information on tickets, though the blog post from the Dota team says they'll be available soon.
If you want to enter the tournament you'll want the Open Qualifiers, which any team can enter and which will take place between October 6 and 9. Two teams from each region will then be invited to enter Regional Qualifiers, which will take place between October 10 and 13. Some teams from the Regional Qualifiers will then be invited to take part in the Major. Registration is here.
At each stage some teams will get invitations without having to qualify through the previous stage, and these will go out on October 5. If you think you're part of this category, then make sure you don't change your roster after September 5 or you'll have to enter the Open Qualifiers like everyone else.