How Do I Use Weapons

[Blackhole123]

Ok, it's been a super long time since I've played.  I only use demo, but I remember having the ability to use weapons.  The thing is, I can't remember how to get them.
Can someone please tell me how.
P.S.  I've looked around in all the help things but couldn't find it. 

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[Starcraftman]

Use a wrench and hit a brick and make it create a weapon. Walk over it, press q and use scroll wheel to select.