Fiscal policy is concerned with the manipulation of government income and government expenditure to influence the level of aggregate demand in an economy. When adopting fiscal policy measures, a government will usually influence the level of aggregate demand by changing tax rates and government spending. Expansionary fiscal policy can be employed when an economy is in equilibrium below the full employment level of output (i.e a recessionary gap).
Should a government decided to employ expansionary fiscal policy, it would ideally run a budget deficit and increase government spending and also cut taxes. This would in turn increase consumers marginal propensity to consume, as tax cuts mean they would end up with more disposable income. This would shift aggregate demand outwards and push the economy to equilibrium that is closer to full employment.