When a person is being forthright, they're being direct, clear, or even straight-up. The opposite of forthright might be evasive, shifty, indirect, or circuitous. But we're not here to talk about those. We're here to talk about forthright.
For the most part, people really appreciate it when others are forthright. It's so much easier to understand what someone wants when they just come out and say it. However, being direct and honest and saying what you really mean isn't easy for everyone. For some reason, a lot of us can be embarrassed to say what we want, and we spend our entire lives learning how to be forthright. A simple way to remember what forthright means is this: if you bring it "forth," it will be "right."