Try not to spend anymore than $100 altogether.
I got my bank credit card when I was eighteen or so (one and a half years ago) from my bank. It has integrated SPC and one Air Mile for every 20$ spent on the card. I now have around 750 or 800 Air Miles amounting to about 12,000$CAD in purchases over the last year and a half.
My first purchase was about 350$ - this small Acer computer and a laptop bag on Clearance at Staples. I also bought a RAM upgrade that I did in-store (to the awe of the employees lol)
But you're right. Never buy more than you can purchase through cash/debit, and always keep an eye on that balance. It's very easy to overspend on a credit card without even realizing it simply because you can't see that balance and may misjudge how much you've actually blown already.
There was a month I was almost in trouble. My credit limit had been boosted to 1,000$ because of an error in payment that left me broke for four days (I had paid the 500$ in my bank account and for some reason, it took four days to go through.
It never does that so it was hard to plan around it). I had purchased to make and food to buy so I had to boost my limit. That somehow led to spending another 700$! I think I bought some furniture, but it was risque and I almost couldn't pay it all back on time lol So just be very careful because even the best budgeters can get caught in the trap :P
You have about 21 days from a statement to pay it back in full before interest tacks on.
Also, on another note, I use my credit card mainly for online purchases but also because my debit card has a per-month transaction limit of thirty that I typically use just through bank transfers and bill payments. Mastercard wants you to spend so they don't limit your transactions per month, which means I can avoid any sudden 1$/transaction fees for going over my limit.
:) Just be smart, and as someone else said (Mac?), don't spend more than you actually have on-hand. If you can't pay it with cash or debit, don't buy it.