I want to ask about the transfer speed of the memory card. It is written on the memory card as something like 45MB/s, 80MB/s. Does it affect anything when we take pictures? What I understand is that the higher number we use, the more rapidly we can take pictures, so it is good for continuous shooting. Is that right? Is there anything else?
Most cameras have an internal buffer they write the pictures to first. From there, the images are written out to the (much slower) memory card. So, if you take pictures at maximum speed, your buffer will be full after some time (My Canon EOS 60D can make about 50 JPEGs or 12 RAW images until the buffer is full).
After that, I have to wait until at least some images have been written out to the memory card. And that process will be faster if the write speed of the card is faster.
Also note that some cameras cannot take advantage of the highest speeds of the cards. My 60D e.g. cannot use the highest speeds, so I stick to class 10 cards (meaning 10MB/s write speed)
So, continuous shooting is not possible, and the breaks between the bursts will be shorter the faster your card (and camera) is.
There are two speeds and it is critical that you separate them:
Make sure you are looking at the write speed to determine who fast a card is for shooting. Still, there are bottlenecks on along the path which means that you will rarely get out the maximum cards-speed for reading or writing: