To paraphrase means to put someone else's ideas in your own words and including a citation to the original source.

Here is an example of a paraphrase (in student's paper):
Climatic influences are evident in other Arctic tundra and heath systems where global warming induces declines in lichen biomass and abundance as a function of increased abundance of vascular plants (Cornelissen et al. 2001).

This excerpt contains a citation which tells the reader that ideas from a source written by Cornelissen and others are being described. If the reader wanted to find out what source is being discussed, or find the source themselves, the full information at the end of the paper would show the following:

Reference in CSE Style (at the end of the student’s paper):
Cornelissen JHC, Callaghan TV, Alatalo JM, Michelsen A, Graglia E, Hartley AE, Hik DS, Hobbie SE, Press MC, Robinson CH, et al. 2001. Global change and arctic ecosystems: is lichen decline a function of increases in vascular plant biomass? J Ecol 89(6): 984-994.

Here is another example of a paraphrase:

Original paper:
I studied wolves and their primary prey, muskoxen (Ovibos moschatus) and arctic hares, in the Eureka area of Ellesmere Island (80° N, 86° W), Nunavut, Canada…My findings for 2000 – 06 suggest that the wolves still depend on both hares and muskoxen, but that hare numbers more reliably determine wolf numbers.

Paraphrase (in student's paper):
While arctic wolves consume muskoxen as part of their diet, the growth or decline of the local wolf population is more consistently predicted by the wolves’ other prey, the arctic hare (Mech 2007).

Reference in CSE Style (at the end of the student’s paper):
Mech LD. 2007. Annual arctic wolf pack size related to arctic hare numbers. Arctic 60(3): 309-311.