What is the purpose of Netherrack? How do I build a nether portal and activate it? I have tried to activate the portal, but it doesn't work; it just burns out.
When lit on fire it remains on fire unless doused with a water block. It gives The Nether a bore hellish feel to it with fires not going out. It can be mined and brought back to the normal world and used to create fires that don't go out, like creating smoke from a chimney. Other uses include light sources or a tunnel that leads to a Nether Portal and have it slowly get covered in Netherrack.
It can also be smelted to make Nether Brick which can be crafted into their block from which can then be crafted into the Fences, Stairs and Slabs used in Nether Fortresses.
Other than that it's only to make thing look "underworldly" like in the normal world (like making a Demon Lords lair which inside has Nether Portal to his Nether Fortress)
To build a Nether Portal you need Obsidian, minimum 4x6 frame(You are able to build bigger portals by increasing either width or height.), and if short on obsidian, you can cut off the corners. Next you activate it with a Flint'N'Steel to spark a fire. Portals can be deactivated using water.
When I build a portal I build it upright and not laying on the ground so if your building the frame so it's laying on the ground then try building it up, I have not ever seen a portal laying down on the ground activated but I only ever build upwards because I always build around it to represent the Holy Grail from Fate/Stay Night and the Nether is the Void Avenger has transformed into another world so "All the World's Evil" has become an evil world of hell, with that I need it upright for the stairs leading up to the sky where the void opened.
For a neither portal:
It is built as a frame of Obsidian (4x5 minimum, 23x23 maximum), after which the inside of the frame is ignited to activate it (flint and steel).
Netherrack (formerly known as Netherstone), is a block that is the most abundant non-air block in The Nether. It has a texture similar to cobblestone, but pale red. When lit on fire, it burns indefinitely.