what is the difference between the prefixes iso,neo,sec & tert

Prefix iso is used for those alkanes in which one methyl group is attached to the next to end carbon atom (second last) of the continuous chain.

Example isopentane is CH₃CH(CH₃) - CH₂CH₃

Prefix neo is used for those alkanes in which two methyl groups are attached to the next to end carbon atom (second last) of the continuous chain.

Example neopentane is CH₃C(CH₃)₂ - CH₃

Prefix sec- is used for those carbon atoms which are joined to two other carbon atoms.

Example 

           I

CH₃ -CH-CH₃

Prefix tert- is used for those carbon atoms which are joined to three other carbon atoms.

Example 

           I

CH₃ -C-CH₃

           _I

          CH₃

iso and neo are basically used for alkyl groups and sec and tert are used for carbon atoms which have functional groups, charge or are radicals.