Very noobish question

My inventory is almost full. Is there a place to stash them? How do I discard items?

You can purchase storage in an Xunlai Chest by talking to the Xunlai Agent, You can just drag and drop them in there, or go to a merchant and sell them.

Ah okay. thanks!

if you are in pre-searing (the very start of prophecies), then there will be no xunlai chest available until you go to post-searing. you can drop your items on the ground (they will be deleted once you zone), put them into your trash bin that is in your inventory, or sell the items to a merchant.

you can open up a zulani account for like 50g, but that is only if your in post-searing or in another campaign

1. storage

2. merchant

3. people

4. other characters (through storage)

5. drop on the ground outside.

Or you can use a Salvage Kit and turn them into materials, which also can be put in storage on the Materials Panel.

You can buy a belt pouch, two bags and then upgrade the bags with a certain rune, for 25 more inventory spaces.

Basics about the inventory: http://wiki.guildwars.com/wiki/Inventory

Everything about containers (every container have their own page too): http://wiki.guildwars.com/wiki/Container

About the storage: http://wiki.guildwars.com/wiki/Vault_box

This summarizes it pretty well.
6. use the trash bin.

um there is also a trash bin on in the inventory window. It is the white thing on the far right where the icons for the inventory bags are.

If you typed /bonus and you have bonus weapons that your toon can not use then you can NOT drop them on the ground to get rid of them as they are undroppable. You can not give them away either as they are untradeable. You can not sell them to the merchant as they are unsaleable. SO you must put them in the trash bin to free up space in your inventory.

I would never recommend just dropping things on the ground cause if you accidentally drop something that you want and someone else picks it up...you could loose that item forever.