What do I do if I feel there are many things which need to be learnt to do my research?
so have others experienced this? 


Basically every smart person feels like that when starting their studies. The majority of the people for which this is not true are usually not the second coming of Terence Tao or Dr. Sheldon Cooper, but simply affected by the Dunning-Kruger Effect. You are not supposed to know everything, and in fact you never will. You already have a head start on your colleagues, who have simply not yet discovered (or wilfully ignore) that they do not fully comprehend many of the seminal papers in your or related fields. You, at least, can work on this in order to produce better research.


  what is the best way of getting around this?


There is no getting around this. To paraphrase the title of your question, many things are to be learned. That's part of doing a PhD. The trick is to learn what you will really need for your research, and to not get lost in the things that are interesting but ultimately not relevant to you. This requires some experience. Hopefully, your advisor or a postdoc will put you on track of what to focus on for now.

As funny as the advice mentioned by @dgraziotin above sounds - in practice, what you really need to develop is a good mental filter to select the 15 or so papers from a 30k papers field that are really relevant to to you.