Plant taxonomy enables the sharing of information about plants. Initially, people use local names for plants, but sharing information makes it necessary to use names that are understood worldwide. This requires developing an approach to naming plants that can be used worldwide, including by people who speak different languages. Plant taxonomy is not about knowing many scientific names; it is about understanding why scientific names are useful and determining the correct name for a particular plant.
There is widespread agreement on the general approach to naming plants. The first step is being aware of the many different kinds of plant, including understanding how they differ. The next step involves using this information to classify plants into groups. Naming a plant is the final step because, in plant taxonomy, its name depends on its classification. This dependence makes understanding how plants are classified of fundamental importance to exchanging information about plants. Consequently, understanding plant classification and determining the correct name for a plant are core components of plant taxonomy.

Resources page for plant taxonomy

All the resources shown are free. When using them, be sure to give appropriate credit. Some come from Wikipedia. The quality of its pages varies. Many provide excellent overviews of their topic; others are very limited; some may be out of date, but it is my first stop when trying to learn about an unfamiliar topic.
History of Botany Wikipedia.
OneZoom: An interactive site for exploring the Tree of Life
APGIV: An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV.
GBIF: Global Biodiversity Information Facility: For global information on the distribution of biodiversity. The data come from different sources.
OpenHerbarium: A website that aggregates and displays specimen data from herbaria and provides “taxon pages” that provide information and images for individual taxa.
ICN: International Code of Nomenclature for algae, fungi, and plants.
ICN-CP: International Code of Nomenclature for cultivated plants.
POWO: Plants of the world online.
IPNI: International plant names index.
Index fungorum: List of names and synonyms of fungi.
CoL