が is a finger, not a topic

Where the picture shows up in が

1. 1

   the one picked out

   私が行きます。

   watashi ga ikimasu

   I'll go.

   は raises a topic; が picks one person out of the others — I'm the one going.

2. 2

   what just came into view

   あ、雨が降ってきました。

   a, ame ga futte kimashita

   Ah, it's started raining.

3. 3

   the part that hurts

   朝から頭が痛いんです。

   asa kara atama ga itai n desu

   My head has been aching since this morning.

4. 4

   what the mind turns to

   日本語が少し分かります。

   nihongo ga sukoshi wakarimasu

   I understand a little Japanese.

   分かる, 好き and 上手 take が, never を.

5. 5

   what is standing there

   この先にコンビニがあります。

   kono saki ni konbini ga arimasu

   There's a convenience store just ahead.