on ebay or online
in a lego halo box or set
there would be instructions in the box that comes with there should be a manuel that comes with. every lego had a manuel
If you want instructions for any sort of Lego creation (that isn't owned by Lego) then I'd just search it and look at the first couple of links. I know that quite a few people have made Halo Lego on Moc-Pages and on personal sites. Try the related links below. Saber-Scorpion (need to buy instructions from store) Mocpages (doesn't have instructions) YouTube (IS instructions)
You can find custom LEGO instructions inside of every pack of LEGOs. There are web sites where you can find custom LEGO instructions such as: Rebrickable.com Worldbricks.com Brickshelf.com LEGO Digital Designer Gallery See Related Links!
Watch YouTube simply
walmart
buy the set at a store from megablox it has instructions in there
There are no Halo LEGO sets, so there are inheritly no instructions. Mega-Blocks got the rights to Halo (to build children's toys) 5 years ago, and have been dutifully building sets since then.
they dont have it for lego, but theres a thing like legos and it cost from $20 to $40 dolars depending where you buy it.
Lego doesn't sell Halo products. That's Mega-Bloks thing. But their Halo theme is usually found in Toys R Us, Target, or Walmart.
on the internet
You either need the right pieces and try to build it. Or you can buy one from Mega Bloks.