Nobody is going to be able to help you unless you provide the exact part(s) of Einstein's 1905 paper on SR that you don't understand.
I know this stuff is tough, but simply saying you don't understand it without saying the exact part of the paper you don't understand doesn't give us enough information to help you.
Have you considered my suggestion of reading an introduction to SR written for the general reader, perhaps even the one Einstein himself wrote, before tackling the original paper?
Above all, don't get frustrated. Most people know little or nothing about SR, and unless you design particle acclerators, or you are a professional astronomer, or design GPS system, or are a particle physicist - which is about 0.01% of the population - you don't really need to know anything about it. If SR is frustrating you, try to learn something different.