As the name suggests, declaration bowling is the strategy used by the fielding side to make the batting team declare. This is often done by bowling poor deliveries, such as full tosses and long hops.
The whole idea of the declaration bowling is to make the batting side score runs quickly (and thus steering the opposite captain to declare the innings). In such a scenario, both the teams get an even chance of winning the match, which otherwise would've headed to a draw. Needless to mention, such a strategy can be seen only in the first class cricket and very rarely, in international Test matches. The reason being, the risk of losing a test match in the context of a series is far greater.
For this purpose, non-specialist bowlers are used. This is done to maintain the bowling figures and also, the dignity of the regular bowlers. This strategy might result in a complete opposite result at times too, especially when the batting side has put a Herculean score.
In 1983, 22-year-old Steve O'Shaughnessy smashed a century in 35 minutes while batting in a County Championship match for [Lancashire][1] thanks to such tactics used by Leicestershire on the final day of a rain-affected match. However Lancashire did not declare before bad light sent the players scurrying away and the game did not resume again, ending in a draw. It's a record that doesn't count and put only as a footnote of any respectable cricketing record book including the Wisden.
[1]: https://www.sportspundit.com/cricket/teams/690-lancashire-county-cricket-club