You cannot make a natural End Portal in Survival
Find a Stronghold
Locate the End Portal room
Place Eyes of Ender in all 12 portal frame blocks
Enter the activated End Portal
In Creative mode, place 12 End Portal Frame blocks in a 3×3 ring
Rotate each frame block so the green socket faces inward
Insert 1 Eye of Ender into each frame block
Step into the completed portal to travel to The End