In act 2, scene 2 why does Romeo not tell Juliet he's there at the very beginning? What is he doing instead?

In act 2, scene 1 of Shakespeare's Romeo and Juliet, Romeo is walking home after meeting Juliet for the first time at the Capulet's party. He decides that he has to talk with Juliet:

ROMEO: Can I go forward when my heart is here?Turn back, dull earth, and find thy centre out (2.1.1–2)

Romeo impulsively jumps over the Capulet's garden wall and finds himself in the Capulet's orchard, which, unbeknownst to Romeo at the time, is just below Juliet's bedroom.
Mercutio and Benvolio are passing by in the street outside the wall, calling for Romeo and making fun of him. Romeo ignores them, and Mercutio and Benvolio continue on their way, ending the scene.
Scene 2 shifts to the orchard, where Romeo mumbles to himself:

ROMEO: He jests at scars that never felt a wound. (2.2.1)

A light suddenly appears at an upstairs window.
Yikes! We can imagine Romeo ducking behind a tree until he knows who's at the window.

ROMEO: But soft! What light through yonder window breaks? (2.2.2)

Juliet appears at her bedroom window (or on the balcony outside her bedroom, depending on the scene design for the play).
It's her! It's Juliet!

ROMEO: It is the East, and Juliet is the sun! (2.2.3)

Romeo goes on about the sun and the moon for a few lines, then tells us something we've already pretty well figured out:

ROMEO: It is my lady; O, it is my love! (2.2.10)

Romeo is still hiding behind the tree, looking at Juliet.

ROMEO: She speaks, yet she says nothing. What of that? (2.2.12)

Yes, what of that? What's he talking about? Juliet hasn't said anything.

ROMEO: Her eye discourses . . . (2.2.13)

Oh. She's not really saying anything. She's just looking around at the sky.

ROMEO: . . . I will answer it. (2.2.13)

Answer what? She didn't say anything. Nevertheless, Romeo quickly steps out from behind the tree—and just as quickly changes his mind, and ducks behind the tree again.

ROMEO: I am too bold; 'tis not to me she speaks. (2.2.14)

Good excuse.
Romeo talks to himself about Juliet's eyes, and her cheek, and her hand on her cheek, and about being "a glove upon that hand, That I might touch that cheek!" (2.2.24–25)

JULIET: Ay me!
ROMEO: She speaks. (2.2.26–27)

This time, she actually does speak, but Romeo is still hiding behind the tree, talking to himself about how great Juliet is.
Then Juliet speaks the famous lines . . .

JULIET: O Romeo, Romeo! wherefore art thou Romeo?Deny thy father and refuse thy name!Or, if thou wilt not, be but sworn my love,And I'll no longer be a Capulet. (2.2.35–38)

Now she's talking about him, which would be a perfect time to speak to her, but he still can't work up the courage.

ROMEO: Shall I hear more, or shall I speak at this? (2.2.39)

While Romeo is deciding what to do, Juliet keeps talking, and says another famous line . . .

JULIET: . . . What's in a name? That which we call a roseBy any other name would smell as sweet. (2.2.45–46)

Romeo is still behind the tree, deciding things.
Finally, Juliet says,

JULIET: Romeo, doff thy name;And for that name, which is no part of thee,Take all myself. (2.2.49–51)

That's Romeo wanted to hear! He gathers his courage, stands up straight, tucks in his shirt, steps out boldly from behind the tree, and talks to her.

ROMEO: I take thee at thy word.Call me but love, and I'll be new baptiz'd;Henceforth I never will be Romeo. (2.2.52–54)

Finally! But after Romeo works up all that courage to talk to her, she doesn't even know who he is!

JULIET: What man art thou that, thus bescreen'd in night,So stumblest on my counsel? (2.2.55–56)

Romeo talks around the answer to her question for a little while, but she eventually recognizes his voice, and they continue with what's considered to be one of the best love scenes ever written.
If we look at a scene in terms of what real people might think and do and say in the same situation, it's not difficult to imagine what's going through Romeo's mind after he climbs over the garden wall and unexpectedly find himself with the woman he loves.