Head = head of the household. All the relationships are linked to him, so for example dau = daughter, gson = grandson
Fan/Tom is the name of the boarder. It is rather mangled, so Fan and Tom are my best guesses as to what is written
The reference (RG13 etc) shows whereabouts within the census you can find this entry, so anyone else who wishes to look it up can do so. Censuses were taken every 10 years from 1841, and apart from 1841 and 1851 have different codes. HO107 were 1841 and 1851, RG9-1861, RG10 - 1871, RG11 - 1881, RG12 - 1891, RG13 - 1901
Hope that helps