Grid Movement
Source Player Core pg. 413
If an encounter involves combat, it's often a good idea to track the movement and relative position of the participants using a Starfinder Flip-Mat or some other form of grid to display the terrain and miniatures to represent the combatants. When a character moves on a grid, every 1-inch square of the play area is 5 feet across in the game world. Hence, a creature moving in a straight line spends 5 feet of its movement for every map square traveled. Difficult terrain can make some squares cost more of your movement.
Iseph Seeks, and a control panel catches their eye to the north, so they decide to move toward it. They spend 5 feet of their Speed to head east. However, the debris is difficult terrain, so each dotted square costs 5 more feet of Speed. Iseph moves diagonally, spending 10 feet of movement since this is an odd-numbered diagonal. They want to move northeast again, but that would cost them 15 feet (10 feet for an even-numbered diagonal and 5 more for being difficult terrain). Instead, Iseph decides to move directly north. This costs them 10 feet, so they've used all 25 feet of their Speed and are out of actions.
Diagonal Movement
Source Player Core pg. 413
Because moving diagonally covers more ground, you count that movement differently. The first square of diagonal movement you make in a turn counts as 5 feet, but the second counts as 10 feet, and your count thereafter alternates between the two. For example, as you move across 4 squares diagonally, you would count 5 feet, then 10, then 5, and then 10, for a total of 30 feet. You track your total diagonal movement across all your movement during your turn, but reset your count at the end of your turn. The diagram in the sidebar below shows an example.
3D Movement
Source Player Core pg. 413
Most movement in a game can be represented on a flat map. If creatures are flying, swimming, or otherwise moving through three-dimensional space, see the advice in the sidebar under Aerial Combat.