Logging in after installing underConstruction

Hi, I am completely new to CSM systems and website building.

After a disastrous first attempt at using wordpress to build a website, I have had to uninstall the program and start over. I am preparing to install everything and go live for a second time, but will need to use the underConstruction plugin when editing material (I think setting up a system to work offline will be too complicated for me).

Last time I installed a plugin of this nature I could not manage to log into the dashboard of my site afterwards. Looking on forums I see that other people have had the same experience with underConstruction.

A lot of technical language is used – ‘white list'(?) and FTP or something. I don’t know what these things are, but I would be grateful if someone could clarify for me (in very simple terms) exactly what I would need to do to make sure I would not get locked out in this way or equally, how to rectify the situation if it happened.

Many thanks and apologies for the lack of knowledge.