Yes, actually. You can.
By copying images in manga, u r familiarizing yourself with the structures & designs of manga-style art. That is how I learned. I am rather good at drawing manga-style, but I am nowhere near good enough for to even think of becoming a manga-ka.
If u want to take ur skills onto a whole other level, I suggest purchasing the ''How to draw manga'' series, & practicing. The books r somewhat expensive, but well worth it. You can also find some of them in libraries, I believe.
Also, if you're able to buy things online, I suggest shopping at ''Borders Marketplace''. They sell quite a few books from the series at prices that range from $3-10, when the original pricing is $20+.
Good luck!