OH OH OH.
Let me explain u a thing about Tumblr. And don't worry, I was quite lost on it too, at first, like I didn't even use it for a year because I never understood how to work it.
Unfortunately it's very difficult to get your stuff seen unless you have followers. Your "dash" or the home page after you've logged in, works just like Facebook or Twitter. The posts on your dash are from the blogs you choose to follow (with the occasional promotional post), and anyone following you will see your posts on their dash.
The key to a successful Tumblr post is getting it A) seen, and B) reblogged. "Reblog" is basically a retweet, and when someone reblogs your post, it is then put on the dash of everyone following them. And then several more people may reblog it from them, which posts it to all the people following them, and so on. So posts can actually go viral really freaking quickly.
Tags are where it's at, and unfortunately it's just one of those things where you have to snoop around Tumblr and observe for a while before you start to see the trends and patterns, although recently they added a feature where popular tag option come up when you're typing them in. But tags are everything, especially if you're just starting out and don't have any followers.
You can have a nearly unlimited amount of tags, so feel free to use them all because without followers, that's the only way people may find your post. When tagging, type in a word or phrase and click the enter/return key and you'll see the word turn into a grey hashtag. Tag it with everything you can think of (why not? xD) and then search and find some blogs similar to you and your interests. Follow them, see what they post, and if they have an Ask Box / Ask Page, click on it and send them a polite message! Explain you're new and need some exposure and ask for a shout-out! Most users are super nice and can publish your message and tell their followers to check you out!
ALSO!! I HIGHLY RECOMMEND --> click on the gear symbol at the top of your dash to access your settings, and turn your ask box ON so that people may send you messages. Once you do, a Tumblr bot will automatically send you a silly question so that you can see and learn how to answer it and how it looks when you post the answer!

That can be very helpful but a lot of people don't find that option when they first start out! (it's default setting is to be off)
AND ONE MORE THING.
I didn't even learn about this until my friend taught me how to work it, and since then my blog has become much more active and popular. QUEUE your posts (make a few initial posts right away, however, so when people look at your blog page it won't be blank) because consistent and active blogs are 100% more likely to be followed! The queue section WON'T appear on the side of your dash until you put something in it first - so when you write a post, underneath (by the tag section) it will say "Post" and you can click the arrow for more options, like "Queue" or "Schedule". If you click queue, it will say that it has been posted in your queue and refreshing the page will allow you to access it!
On your queue page, it's very simple. You choose a time frame (from ___ to ___) that you want your posts to be automatically published, and you choose how many posts per day you want. Then it automatically calculates the exact time/date each post in your queue will be published based on your settings! <3 And it even TELLS YOU, so you can easily see if your posts end up getting published early in the morning or late at night.