I started to write my own original sentences using the gramm

using the grammar (that) I was learning
是现在分词短语作状语.
I was 前是省略了一个that
using the grammar I was learning这个分词短语作状语,前不用加介词by.这是个现在分词短语,如果换成一个过去分词短语,比如used the grammar I was learning,比较下就会发现加介词by不合语法.
介词后面是跟动名词,而动名词只能作主、宾、表语.
今天有时间,虽然没分,但还是详细的跟你说说.

可以这么说

using之前实际省略了that was，that 代sentences用我学过的语法造的句子
后面是对的I was 前省略了that/which
by doing sth.一般指做某事为止，或者被。。。
本句用by完全不对