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DNA is double stranded, made up of sugars known as deoxyribose, nitrogenous bases (A,T,C,G) and phosphate group. The phosphate group is always bonded to the 5 prime carbon of the sugar. The 5 prime simply means the carbon number in the deoxyribose ring (deoxyribose sugar is in a pentagonal ring with 4 carbons in the ring, one oxygen in the ring and CH2OH {which is the 5' carbon attached to carbon number 4 of the ring}). 5 prime carbon in the just the carbon that's the fifth carbon in the deoxyribose ring.
Each strand of the DNA in the double helix is called polynucleotide strands and one runs from 5 prime end to 3 prime end and the other strand runs from 3 prime end to 5 prime end (just the opposite). The 5 prime and 3 prime are nothing but the names of the carbon to which the phosphate groups are attached to.
From a genetics book, "At one end of the strand, a free phosphate group is attached to the 5 prime carbon atom (carbon number 5 of the ring) of the sugar (meaning the deoxyribose sugar) in the nucleotide. This end of the strand, referred to as the 3 prime end, has a free OH group attached to the 3 prime carbon atom of the sugar."
So, what all this is saying is: one phosphate is attached to carbon number 5 of the deoxyribose sugar ring, and another phosphate is attached to carbon number 3 of the same deoxyribose sugar ring. If you look at figure posted by savio, you can clearly see that the 3 prime to 5 prime strand (the right strand) has flipped deoxyribose sugars, so the 3 prime to 5 prime strand is antiparallel to the 5 prime to 3 prime strand (the left one).
As bio_man already said, a polymerase reads from 5 prime to 3 prime. So, we can suppose the 5 prime to 3 prime strand to be the orginal template and the 3 prime to 5 prime strand be just a complementary strand. We, you could flip the 3 prime to 5 prime strand to get 5 prime to 3 prime strand.
If you have a 5 prime to 3 prime strand with bases ATCGGC, then the complementary 3 prime to 5 prime strand will have the bases TAGCCG, or the flipped 3 prime to 5 prime strand will give GCCGAT. This is a little complicated but when we are talking about genes, we are only talking about a certain section of DNA, so, we don't consider the whole strand. For your question regarding whether the 3 prime to 5 prime strand will give the same result as the 5 prime to 3 prime end, well its a bit complicated:
Firstly, a DNA strand, the 5 prime to 3 prime strand, will transcribe mRNA. You might know about the start and stop codons and all that. The mRNA will be complementary to the template strand (the double strand DNA splits into two strands, the 5' to 3' strand will transcribe complementary RNA strand and this RNA will further go on to translate amino acids and finally into proteins.)
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