Judging by your comments, you seem to have issues understanding the action economy in 5e.
Every creature in 5e can move up to their speed, take 1 action on their turn, and potentially take a bonus action or a reaction. Some features can change this so that you can move further, or take additional actions. Haste would be an excellent example since it increases your movement, and allows you to take an additional (albeit more limited than normal) action.
Either way, you can only ever take 1 bonus action during your turn, but to do so, you need to have access to a feature that allows you to take a bonus action. Pretty logical if you think about it - if there's nothing you can do with a bonus action, then obviously, you can't "spend" it on anything (duh).
Flaming Sphere is one such option, a rogue's Cunning Action or the Heat Metal spell are others. You can also use your bonus action for two-weapon fighting, see PHB p. 195 for details.
Now, Flaming Sphere allows you to take a bonus action to move the sphere, and potentially deal damage. For the duration of the spell - including on the same turn that you cast it, since nothing says otherwise - you can use this bonus action, provided that you haven't used your bonus action for something else on that turn already.