A statute is a codified or written law that has been properly passed by a legislature (usually by a simple majority vote) and then promulgated to the public, usually by publishing it in an appropriate forum. It differs from a constitution in that it may be freely amended or revoked by a further vote of the legislature. It differs from a regulation in that it requires a full session of the legislature to change. Most of what we think of as law is contained in some statute.
In common law systems, a statute can overrule a general principle of the common law. For example, water resources acts passed by several legislatures in the last half of the 20th century did away with the common law concept of riparian rights - rights related to the flow of water. However, most constitutions prevent legislatures from passing laws that interfere with judicial independence, such as prohibiting a bill of attainder - a statute ordering imprisonment or a fine.
Governments publish statutes as they are passed and they are often consolidated with their amendments on a regular basis. Although this practice continues, the advent of the internet has allowed most governments to publish and update their laws on-line.