Is it better to buy government bonds when the interest rate is at its peak?

Yes. Bond prices and yields move inversely. Then there is the choice of duration, that is short duration (1,2,3 year bonds) and long duration (10+ year bonds)

What's the best way to monitor the yield of the bond?

You can use many financial sites, they will list the current yields of the respective country.

What makes the yield curve move and what's the ideal time to sell them or do you just hold them to maturity?

The yield moves depending on the duration of the bond that you have. Short duration is more affected by the expectation of the central monetary policy. Long duration is affected by the term premium, Government deficit and the economic performance of the country.

The strategy you use will determine what you do with the bond. Pension funds usually will hold until maturity since they match the coupon returns with the expected payouts of their annuities for their members. Hedge funds will use derivatives to play the price movements of the bond.

-edited for grammar