how i link individuals across different census? ie., look at one individual in 1930 and then again in 1960?
Unfortunately, this sort of task is not possible with the long-form decennial census public use micro-data available via IPUMS USA for several reasons. First, the long-form census sample only gathers information on a fraction of the US population. Therefore, it is quite unlikely that the same individual will be included in multiple decennial census samples. Second, the US Census goes to great lengths to ensure the confidentiality of respondents in the public use micro-data. Both of these factors make it impossible to link individuals between decennial census samples.
With that said, there is an exception. IPUMS USA has a number of linked samples from 1850-1930. This is made possible due to the presence of full-count census samples in these years. I am not sure if this sort of time-frame is what you are looking for, but it might be helpful.