What lobbying registers track
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A lobbying register records who is being paid to advocate on behalf of a client to influence government decisions, typically listing the lobbyist, the client they represent, and often the general subject matter of their advocacy, which is central to how the system actually works, as a closer look usually confirms.
These registers exist because lobbying itself is a legitimate part of policy making, giving officials access to expertise and different perspectives, but the activity becomes harder to assess fairly if it happens entirely out of public view, though the practical effect can vary considerably, a point that becomes clearer in hindsight.
By making this activity visible, a register allows journalists and citizens to see which interests are actively engaging with government on a given issue, which is a useful starting point for understanding how a particular policy debate is being shaped, which is one reason the subject remains contested.