Does anyone know what this plant/weed is?

Looks like one of the Hypericums (St John's Wort) to me. If you haven't yet seen them, it will have yelllow flowers.

have their leaves arranged alternately, not opposite (as in the OP's picture).

Thank you so much for your comments, I think it might be Hypericum. I will be watching out for the yellow flowers to confirm. I hope it isnt deadly nightshade, just read about it and am scared!

Why would you be scared of deadly nightshade? Do you make a habit of picking weeds and eating them?

I only eat weeds I can positively identify. For instance, when I weed in the spring, I pluck wild radish sprouts, rinse them, and add them to salads. Stinging nettle is said to make a good soup, though I haven't tried.

Actually, I do. Many common garden weeds are edible, delicious and just as (or more so) nutricious as commonly grown greens.

Nettle makes a delicious potherb, much better than spinach IMO.

A friend of mine offered me some weeds to grow indoors. I am currently growing them now but they give off a very strong odour which fills the house. Im not sure what variety they are but they have pointy leaves, 7 or 9 on each stem. Any idea what they could be ? Im new to the whole gardening thing so dont really know much about them.

They sound very similar to the WD