Suggestive tag, as it implies, have suggestive scene without any actual sexual activity, like, lucky panty shots, swimsuit scenes, seeing characters almost naked. Basically fanservice stuff.
Erotica tag contains actual erotic content, like the characters engage in sexual activity and it is shown to the audience.
Pornographic, obviously, is simply porn.
The difference between Erotica and Pornographic is the presence of plot in the story. If a story has actual plot and have some sex scene in-between, then it would be an Erotica.
A work solely dedicated to sex scenes and drawn just for the sake of it, is porn/hentai.