At low temperatures an electron that is moving in a metal lattice attracts positively charged atoms (ions) and creates positively charged neighborhoods that facilitate the electron that is near it. Super fast electron flow or conduction.
An excellent site on superconductivity which had been created on the occasion of the 100 years of superconductivity by Ame en Science, CNRS-Physics (French National Centre for Scientific Research), French society of Physics, and the Triangle de la Physique (credits).
Alternatively you could explore the site via its site map (plan du site)
Notes written based on the very interesting page "More details" below that includes two short videos.
Atoms of metals tend to loose electrons and get positively charged e.g. iron rusts because its electrons are ready to take off and bind to oxygen to form an iron oxide.
In the lattice of a metal we have atoms that have lost electrons and have therefore become positively charged ions and we also have electrons (negatively charged) which are moving around.
Atoms (or more correctly positive ions) could be imagined as big balls and electrons as small ones. As we know “opposites attract”.
At low temperatures, the electron while moving will attract the atoms/positively charged ions; as a result a small positively charged “neighborhood” will be created near the electron’s trajectory.
If another electron is close or “is coming behind” the first one it will be attracted by this positive “neighborhood”. The first electron facilitates the second. The second electron actually “teams up” or “pairs up” with the first one which created this “neighborhood”. It is said that the two electrons form a Copper pair. As a result a super fast electron flow or conduction occurs in the metal.
At high temperatures (e.g. ambient temperature) the positively charged ions vibrate very quickly and will not be attracted by an electron passing by. This is why superconductivity occurs at low temperature.