can anyone explain the double indicator as simple as you can and with few details?

The two indicators used are commonly phenolphthalein and methyl orange. Phenolphthalein changes its color when the solution is slightly alkaline, while methyl orange changes its color when the solution is slightly acidic.

A common example of using double indicators is the titration of sodium carbonate solution (in the conical flask) against hydrochloric acid (in the burette).

The first indicator used is phenolphthalein. Hydrochloric acid is added to the sodium carbonate solution. The first equivalence point is reached when all sodium carbonate are just completely changed to sodium hydrogencarbonate.
Na₂CO₃(aq) + HCl(aq) → NaHCO₃(aq) + NaCl(aq)
At the first equivalence point, the solution becomes slightly alkaline due to the hydrolysis of hydrocarbonate ions.
HCO₃⁻(aq) + H₂O(l) ⇌ H₂CO₃(aq) + OH⁻(aq)
At such pH, phenolphthalein changes its color from pink to colorless. This shows the first end-point.

Then, methyl orange, the second indicator, is added to the colorless solution. Hydrochloric acid is further added to the solution. The second equivalence point is reached when all sodium hydrogencarbonate is just complete changed to carbon dioxide.
NaHCO₃(aq) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)
At the second equivalence point, the solution becomes slightly acidic because carbon dioxide gas dissolves in water to give carbonic acid solution.
At such pH, methyl orange changes its color from yellow to orange. This shows the second end-point.