They would need very different musculature from humans and vertebrates in general, and the gait would also be very different.
The locomotory tentacles - two, or three for stability, or four to leverage lateral symmetry - would of course need two or three strong antigravitational muscle fascias to keep the body off the ground and have it "fall" forward. They couldn't apply leverage to a bone or exoskeleton like vertebrate and arthropods do, but they would almost surely evolve a hardened surface (essentially a segment of exoskeleton) to improve grip on the ground; the muscles would then naturally bind to that. To improve flexibility they would have two or three hardened, corny "shoes" on the lower part of each tentacle, joined by flexible tendons.
The gait would be either the awkward movement of clowns with too-long shoes, or more likely they would swipe the legs laterally (two other sets of muscles are required), keeping the tentacle tips bent inwards to reduce the footprint.
The body would fall forward as humans' do, then the hindmost tentacle would swipe to the outside (or to the inside?), sliding forward with minimum elevation, and land on the ground to the front, taking the weight. Having only one section of tentacle as "shoe" would give a wobbly gait like walking on stilts. Having two would achieve a smoother gait, as weight shifts from the back to the front of the same tentacle "shoes".
With two tentacles for motion and two others for stabilization, your alien would be able to run quite fast, sort of a low-altitude flight. In closed environments it could be able to navigate sharp bends at speed way better than a human could, using the other tentacles to pull and push against walls and other support structures.
(a different gait with two slow "treads" under the tentacles of the alien gukuy is presented in Eric Flint's Mother of Demons - the cover image does not match the description).