Can someone explain these to me and how they fit in to relationships and sexual orientation? Probably a lot to ask but I'm a little confused at the moment. Not sure this even makes sense as a question?
If I were differentiating those terms, I'd say: Sexual desire = the "sex drive" or libido. This is an innate, natural craving - like hunger - but for sex. Sexual attraction = is what you feel for another person, whom you find attractive usually due to their physical qualities (but can also be for mental/emotional qualities). Sexual orientation = what gender you are attracted to, whether male, female, both, neither, or other (designated by homosexual, heterosexual, bisexual, asexual being the most used labels). As for relationships? Well usually people start romantic relationships because they're attracted to the other person, and it all goes forward from there as you get to know one another...
I think Kodo's definitions are mostly right, but with the clarification that sexual orientation is what *sex* you are attracted to, because gender is a characteristic that is separate from sex. For example, according to wikipedia, the World Health Organization states, "'ex' refers to the biological and physiological characteristics that define men and women," and "'gender' refers to the socially constructed roles, behaviours, activities, and attributes that a given society considers appropriate for men and women." There are masculine men and feminine men, masculine women and feminine women. And many, many points in between. And folks who are transsexual and transgender.