The poem begins with a metaphor: the speaker is comparing the experience of being in love to a journey, and more specifically to a journey to a place the speaker hasn't been before. This metaphor invites a sense of adventure and thrill into the poem: traveling somewhere new may be challenging and frightening in many ways, but it's also exciting.
It seems the same goes for love, as the speaker is "gladly beyond any experience" he's ever had. In other words, the speaker is fully outside his comfort zone, and yet totally enjoying the thrill of the unknown. (Note that, while we're using masculine pronouns throughout this guide for the sake of clarity, the speaker is ungendered in the poem itself.)
The lack of space between "travelled,gladly" isn't a mistake, but a classic case of Cummings playing with traditional syntax and grammar in his work. Here, the spacing might suggest that the speaker's journey is tied up with his happiness. The enjambment at the end of line 1, meanwhile, evokes this sense of traveling "beyond" the confines of the known, the line itself thrusting out into the blank space of the page.
Next, the speaker tells his beloved that their "eyes have their silence." Eyes are, of course, always silent; the speaker is being metaphorical again, essentially saying that there are things about his beloved that he doesn't understand. This person is somehow mysterious; the speaker can't read them, so to speak, but still feels transported to some exciting new land upon looking into their eyes.
The consonance and assonance in "experience" and "silence" create a subtle echo, as if to imply that the beloved's silence, or mystery, is the reason that the speaker finds himself "beyond any experience." There is something about this relationship that the speaker has never encountered before.