Am I bisexual or am I lesbian?

Only you can know the answer to that. Both labels define sexual attraction, which is a pull toward a particular person in which you feel you want to partake in sexual activities with them. If you identify as female and you feel sexual attraction only toward other female-identifying people, then lesbian might be the right label for you. However, if you, as any gender, feel sexual attraction toward two or more genders, then bisexual might be more appropriate. There are also many other labels that may suit you, such as polysexual (sexual attraction to multiple genders), pansexual (sexual attraction to all genders), asexual (sexual attraction to no genders), or even more specific ones like gray-asexual (sexual attraction in rare, fleeting, or confusing instances) and demisexual (sexual attraction only toward those you've developed a strong emotional bond with). AND they can even be combined -- like demihomosexual (sexual attraction toward those of the same gender you've developed a strong emotional bond with). Sexual attraction isn't the only attraction, either. Perhaps you feel romantic attraction to two genders, but sexual attraction only to other women? Then biromantic homosexual might be the most accurate label. It's a lot of information, and can be overwhelming and confusing. There are a ton of labels out there, because there are so many different people all feeling different things. The good news is, you don't need a label if you don't want one, you don't need to decide on one ASAP, and you can even change your mind in the future if you start to feel differently or discover a label that better suits how you feel. There are even two labels for "I have no idea / this is all confusing" -- wtfsexual and quoisexual. Just remember -- if you feel it, it is valid, even if there isn't a label for it. Labels are made to fit people, people do not fit labels.

If you like men as well as women you are bisexual. As a lesbian you can find men to be attractive but not have any motives other than friendship with them.

That is truly up too you. Some girls may say they're bisexual when in reality they are a lesbian. Some say they're bisexual when they are too afraid to come out while others are actually bisexual. It becomes complicated when you're trying to discover your sexuality. In the end it all comes down to you and how you feel.

Sexuality is often not as simple as labels can make things seem. You can look up a Kinsey score test online and see where your result falls -- although it is a bit outdated in terms of gender identities, it can help you think about your sexuality. You can ask yourself about any past relationships and experiences. Which gender (or genders) were you most comfortable with, which do you fantasize about the most? You can also think about the people you find yourself having crushes on or thinking of most often. Do you notice a pattern towards only those who are female/female-identified or do you seem to have an equal amount with those male-identified as well, or somewhere in between? You may also be bisexual but with a slight preference towards females, etc. Know what a big step in self-awareness and discovery it is to be asking yourself these questions!

I think I am Bi cause when I think of girls nude I get horny and when I think of guys I get horny

That depends on how you feel. If you are sexually attracted to girls as well as guys, you are bisexual. If girls are the only ones you are sexually attracted to and you're not sexually attractive to any guys, you are lesbian.

Bisexuality is the sexual attraction to all genders on the spectrum, Lesbianism is romantic and sexual attraction to women, solely. With finding your sexuality and becoming comfortable with whatever you wish to label yourself, or not, you will figure this out :)

If you like boys and girls either romantically or sexually, you are bisexual. If you don't like boys romantically or sexually at all, then you'ew lesbian. Honestly, you won't figure it out in one day because it's easier said then done. Best of luck for figuring out your sexuality :)

Only you can answer that! But, it may help to know that bisexuality is a spectrum. It can include people who are mostly attracted to the same gender and sort of attracted to other gender(s), people who are mostly attracted to another gender(s) and sort of attracted to the same gender, and people who are equally attracted to both! So, if you want to identify as a lesbian, you can. If you would like to identify as a bisexual, you can! It's YOUR identity, and only YOU can choose the right sexual identity for yourself.

That is really a question that you have to answer yourself. You know you better than anyone else. Just look at yourself and choose what you're comfortable with.