开始 + Noun
我开始了一项新的工作. I started a new job.
我开始 (学) 一本新的汉语课本。 I started (studying) a new Chinese textbook. (not sure if the 学 is required here or not. If include it then its a 开始 + verb + noun structure, but I'm not sure if its correct without).
学 is necessary to clarfy "学" or "写" to aviod the ambiguity.
开始 + Verb
我开始买很多东西。 I started to buy a lot of things.(但是我没有钱!)
我最近开始了减肥。 I've recently started to lose weight.
Correction: 我最近开始减肥了.
Verb. + 了= the action has finished. Basing this sentence, the action减肥 have not finished.
我拿了他的书.
他做了饭.