I would be happy to explain.
ssp. abd subsp. are both abbreviations for "subspecies" which is just below the rank of species.
Usually subspecies are very similar to the species but have a consistently different character in different populations, and this difference is genetic.
Often subspecies have evolved to exploit a specific niche, and are on the way to becoming species in their own right as genetic drift places them further apart from their origins.
Once a subspecies is published, it always creates another subspecies: the original species. Once Drosera filiformis ssp. tracyi was published, it also created D. filiformis ssp. filiformis from which it was split on the basis of a certain different characteristic which the population shares.
Var. is the abbreviation for "variation". It is below subspecies in rank, but above forma. It is reserved for those examples which differ but little from the species, but may have some important variation: a different flower or leaf color for example. Variations may become very successful, and out compete their progenitors: a different flower color might attract a better pollinator, leading to better seed set and dispersal. So variations are always coming up out of the genetic recombination that happens during sexual reproduction. Like a deck of cards: some hands are winning hands, some are losers. The winners pass on their qualities to another generation. The numbers point out if it is a random or successful variation.
The final one f. is the abbreviation for "Forma". There are no legitimate "forma" publications in Drosera. Forma is applied to the least difference in form. It is very much similar to variety, but even more restrictive, and usually refer to a minor quality or character.
Technically you could have a Drosera capensis ssp. erectifolia var. rubra f. hirsttum, except it would never pass review. Most taxonomists work towards lumping things together , vs splitting them apart, which is why there is just D. capensis, and D. spatulata, with no legitimate publications beyond the species level.
The order of rank is aways from the most general qualities to the most specific. Hence, Genus, species, subspecies, variety, and forma in that order.
It is a matter of intense field study to be able to get the feel for what a plant population is doing by way of speciation. These determinations can only come from studying a very large number of individuals within a population. Drosera is such a variable genus that it takes much more than seeing a different looking plant and deciding to simply call it a variety. It always comes down to numbers: how many individuals within a population are expressing a certain trait, and how far does their range extend? Those are essential questions in determining the taxonomic rank within a population.
Hope this helps!