Welcome, Bizob.
Although I'm hardly a guru, I think I can set your mind at ease.
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If you haven't already, go ahead and download the Source SDK in Steam. (Click on the Tools tab, then right-click on Source SDK and choose Install game...)
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Once it is downloaded, double-click it to launch the SDK. Steam will check to make sure it has the latest version before it launches the program. Once the SDK window comes up with its list of apps, you're good to go (even if you just hit Cancel). Now you've got the updated SDK.
Read the postings you see online very carefully. Some people are having trouble loading maps & content they made with the old SDK, using various workarounds. There are various fixes for these problems. But since you're just starting out and you have no maps or anything saved yet, this won't affect you.
Now, if a tutorial tells you outright that it doesn't work in the new SDK, you should probably find another tutorial. Here are a few places to start looking:
Valve Developer wiki: http://developer.valvesoftware.com/wiki/Category:Level_Design
There are lots of useful links on this page. Setting up Hammer, mapping basics, HL2, TF2, and Portal tutorials.
Thinking With Portals wiki: http://wiki.thinkingwithportals.com/wiki/Main_Page
Most of this stuff is still over my head, but there's some basic stuff too.
http://www.interlopers.net/
http://www.halfwit-2.com/
Most Half-Life 2 mapping tutorials are relevant to Portal mapping. Creating geometry, texturing, and lighting are all the same. The game entities differ, though, so be careful trying to implement more complicated stuff from HL2 tutorials unless you know what you're doing.
Have fun!