how did it evolve?
It is built from five separate shield volcanoes that erupted somewhat sequentially, one overlapping the other.
Hawaii (island)
The island of Hawaiʻi is built from five separate shield volcanoes that erupted somewhat sequentially, one overlapping the other. These are (from oldest to youngest):

Geological evidence from exposures of old surfaces on the south and west flanks of Mauna Loa led to the proposal that two ancient volcanic shields (named Ninole and Kulani) were all but buried by the younger Mauna Loa. Geologists now consider these "outcrops" to be part of the earlier building of Mauna Loa.

Because Mauna Loa and Kīlauea are active volcanoes, the island of Hawaii is still growing. Between January 1983 and September 2002, lava flows added to the island. Lava flowing from Kīlauea has destroyed several towns, including Kapoho in 1960, and Kalapana and Kaimū in 1990. In 1987 lava filled in "Queen's Bath", a large, L-shaped, freshwater pool in the Kalapana area. Another 875 acres were added between May to July, 2018 by the 2018 lower Puna eruption.
where did the magma that erupts from mauna loa likely form The volcano's magma comes from the Hawaii hotspot. where is mauna loa? Hawai, U.S. state. what is it? It is one of five volcanoes that form the Island of Hawaii. does anyone monitor this place? Hawaiian Volcano Observatory and Mauna Loa Observatory. what is the above stated hotspot? The Hawai’i hotspot is a volcanic hotspot located near the namesake Hawaiian Islands. is there any theory related tho this? Canadian geophysicist J. Tuzo Wilson proposed the hotspot theory to explain these zones of volcanism so far from regular conditions, a theory that has since come into wide acceptance. how frequently does it erupt? Over the last six million years they have been far higher than ever before, at over per year.
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Hawaii (island) [SEP] Volcanism
The island of Hawaiʻi is built from five separate shield volcanoes that erupted somewhat sequentially, one overlapping the other. These are (from oldest to youngest): Geological evidence from exposures of old surfaces on the south and west flanks of Mauna Loa led to the proposal that two ancient volcanic shields (named Ninole and Kulani) were all but buried by the younger Mauna Loa. Geologists now consider these "outcrops" to be part of the earlier building of Mauna Loa. Because Mauna Loa and Kīlauea are active volcanoes, the island of Hawaii is still growing. Between January 1983 and September 2002, lava flows added to the island.