Guild Wars 2

I have seen people with weapons like flame swords for example.
How do I get weapons like them?

‘Fiery’ weapons you ask?

There’s a sword skin from the hall of monuments (requires a link with Guild Wars (1)):
Fiery Dragon Sword
There’s also a blue version which you can make in the Mystic Forge:
Jormag’s Breath
Then there’s a fiery greatsword which can drop from champion bags:
Cobalt
At one point you could get the skins from Fused weapons from Black lion tickets. They are currently retired:
Fused weapon skins
The dungeon version you can get from the Citadel of Flame is:
Molten Weapons
Then there’s the legendary dagger Incinerator:
Incinerator

Those are some I can think of immediately.

TL;DR
‘Nice’ Weapons can come from:
Rare drops from bosses or champion bags;
Dungeon tokens reward;
Gem store skins;
Mystic Forge recipes.

The Wiki has a lot of image galleries, for example this one of sword skins: http://wiki.guildwars2.com/wiki/Gallery_of_swords

You can find them either by searching for ‘gallery of [whatever]’ or by going to a related page (the sword page for example) and following the links at the bottom. For armor I find it easier to search for just armor and scroll down to the bottom of the page to get the navigation box where they’re divided by race and gender.

From there you can click on the name of any you like the look of to be taken to the page about it, which will tell you where you can get it (including whether it’s on the trading post and how much it costs).

BTW If you’re using this method to choose skins you like I strongly recommend you pick out a few different options (open them in different tabs) before you get too attached to a specific one. It mixes all the skins from the game in together with no indication of how easy or hard they are to get. So you’re just as likely to discover one that costs 2,000g or needs 29,000 achievement points to get as one you can buy from a karma vendor in a starting map. It helps to have a ‘backup’ if your first choice is impractical or impossible to get, and to choose it before you’ve got your heart set on the impossible one.