What is the speaker's mood in lines 1–2 and how does it change when the speaker sees the daffodils?

The speaker is lonely and at loose ends in the first two lines of the poem, which are as follows:

I wandered lonely as a cloud
That floats on high o'er vales and hills

The imagery of being a cloud floating on "high" suggests that the speaker is feeling disconnected and alienated from the world around him. He is drifting and not connecting with his surroundings.

His mood changes dramatically, however, when he sees the daffodils. There are thousands of them blooming in front of a lake and swaying together in the wind. The sight fills him with joy. He says he has no choice but to become "gay," or happy, in such company.

This is a quintessential Wordsworth poem. It celebrates nature and captures a moment of deep emotion recollected in tranquillity, which Wordsworth wrote was the goal of his poetry. In the last stanza of the poem, his speaker ruminates on how much joy remembering the daffodils brings him later on, when he is inside his house in a thoughtful mood. He calls this kind of remembering "bliss." He writes of it:


And then my heart with pleasure fills,
And dances with the daffodils.

In other words, it is the simple pleasures that bring the most joy, Wordsworth says.

Stanza one of Wordsworth's poem reads:

I wandered lonely as a cloud 
That floats on high o'er vales and hills, 
When all at once I saw a crowd, 
A host, of golden daffodils; 
Beside the lake, beneath the trees, 
Fluttering and dancing in the breeze. 

In lines one and two the speaker, or person narrating the poem (not necessarily the author of the poem), explains that he was "wandering lonely." The speaker uses a simile to compare their movement to the movement of a cloud floating above rolling hills. At that moment, a transition happens as he suddenly notices a great number, which he describes as a "crowd" of daffodils. This description of the daffodils as a "crowd" or "host" is an example of figurative language. We know that this isn't literally a crowd, like a crowd of people. Yet, we understand that he is implying that there is a large number of flowers clustered in this spot. 
 
In the first two lines, he describes his mood as "lonely." But when he sees the flowers, he is no longer lonely. Now he is surrounded by a cluster of apparently cheerful flowers, since they are "fluttering and dancing in the breeze." This energetic diction shows the improvement that the flowers made on the speaker's mood. At first he was wandering lonely. The word wandering  implies a slowness of pace; in the same way, clouds usually glide slowly through the sky. However, the flowers are dancing in the wind. This increasing action once more emphasizes the positive progression of the speaker's mood. 
https://www.britannica.com/biography/William-Wordsworth

https://www.poetryfoundation.org/poems/45521/i-wandered-lonely-as-a-cloud