Shabbat Shira is observed during the reading of Beshalach in reference to the Song at the Sea that was sung after the Israelites crossed the sea during exodus.
The Shirat Ha’Yam in the Torah is set up visually differently than most other text. Often readers chant in an alternate melody and perform Hagbah to show the congregation the poetic layout of the text in recognition of its uniqueness. Liturgically, Rabbis often incorporate the singing of Mi Chamocha as part of the service.
Interestingly, There is a Midrashic tradition to feed birds on the weekend of Shabbat Shirah. This tradition comes from the Midrashic interpretation that fruit trees spung from the earth and children fed birds with its fruit when the Israelites crossed the Red Sea. After eating the food set out from the children or possibly the Manna left for the Israelites, the birds then joined in song.
