Registered Retirement Savings Plans (RRSP) and Registered Pension Plans (RPP) are both retirement savings plans that are registered with the Canada Revenue Agency. RRSPs are individual retirement plans, while RPPs are plans established by companies to provide pensions to their employees.
The amount in Box 20 of your T4 - RPP, is only reported once, on the T4 screen in TurboTax. This amount is NOT your RRSP contributions, so do not confuse the two.
If your employer contributes to an RRSP on your behalf, you will receive a separate RRSP Contribution slip and need to report it in the RRSP section. You may see something on your T4 in regards to this RRSP, however, it will be in Box 40 of the T4 and is already included in your income. The tax deduction for your RRSPs which are deducted from your pay and "matched" by your employer will be totalled and shown on the RRSP Contribution slip. Also when you contribute to an RRSP through work, you should receive "two" RRSP Contribution slips, one from March to December, and one for the First 60 Days of this year.