The traditional form 進 = 辶 (chuò, the walk radical) + 隹 (zhuī, a short-tailed bird). The 辶 element on the left is the ancient sign for movement along a road, a foot on a path. The 隹 inside it is a bird, and the old reading turns on a fact of nature: a bird can only ever walk forward, never backward. So the picture is movement that goes ahead and never reverses, which is exactly the sense of the word: to advance, to go forward, to enter.

The simplified form 进 swaps the bird 隹 for 井 jǐng (a well), a tidier shape that is easier to write. The walk radical 辶 stays put, so the modern character still reads as movement on the road, even though the inner element no longer carries the bird image.

Three senses branch from the foot on the forward path:

1. To enter, to go in. Movement across a threshold into a space: 进来 jìnlái (come in), 进去 jìnqù (go in), 进入 jìnrù (to enter).
2. To advance, to make progress. Movement ahead in space or in skill: 前进 qiánjìn (to advance), 进步 jìnbù (progress), 进展 jìnzhǎn (to make headway).
3. To take in, to carry out. Movement of goods or action inward: 进口 jìnkǒu (to import), 进行 jìnxíng (to carry out), 进食 jìnshí (to take food).

The thread through every sense is forward and inward. Whether a person crosses a doorway, a student climbs in skill, or a country brings goods across its border, 进 is the bird that only walks ahead, the foot that moves in and never back. Its standing opposite is 退 tuì, to retreat.

The forward sense of 进 is where the character earns its everyday weight. Step forward in space and you have 前进 qiánjìn, to advance; step forward in skill or condition and you have 进步 jìnbù, progress. The same root powers 上进 shàngjìn, the drive to better oneself, and 进展 jìnzhǎn, the headway a project makes over time. In each the picture is the same forward-walking bird, now climbing rather than merely crossing a threshold.

Its constant foil is 退 tuì, to retreat. The two are so tightly bound that they fuse into single words: 进退 jìntuì (advance and retreat, i.e. one's room to maneuver) and the idiom 进退两难, caught with no good move in either direction. To know 进 well is to feel 退 standing right behind it.

Picture a short-tailed bird on a road, the 隹 inside the walk radical 辶 of the traditional 進. A bird hops only forward, never back, so the whole character is forward motion that cannot reverse. Hold that single image and every sense follows.

Walk that bird across a threshold and you have entering (进来, 进去, 进入). Walk it ahead in skill and you have progress (进步, 前进). Walk goods in across a border and you have importing (进口, 引进). And set 退, retreat, behind it, and you feel the tension that powers 进退两难: the bird that can only go forward, caught at a spot where forward is blocked too.