A good all around size for trout, bass, etc. in small rivers, streams, lakes, etc. would be a 9' 5/6 weight rod. A 5/6 weight single action reel. 5 or 6 weight double taper floating line.
For large rivers, salmon, steelhead, etc. Move up to a 8' to 9' 7/8 weight rod. A 7/8 weight reel with a center drag. 7 or 8 weight sinking tip line. This set up could also be used for saltwater fishing. Casting from the beach, rocks or a boat.
If your interest is to fish small pond and streams. A 7' to 8' 2/3 or 3/4 weight rod. A 2/3 or 3/4 weight single action reel. 3 or 4 weight double taper floating line.
Them there is BACKING. The line on the reel that is used to play the large fish. The fly line is designed for casting but is not normally long enough to fight the larger fish.
Tippet, leader. This goes on the terminal end of the casting line. Usually, 4' to 9' long. Depends on use.Type of water. Depth of water, etc. Have a variety of these available in different weights The fly ties to this.
Do some research before you start buying equipment. You should be able to get a very nice set up for $300.00.
I use a 9' rod, reel with a drag, 5 wt rig with floating line and an 8' rod, single action reel (no drag), 5 wt sinking tip line for lakes and small rivers.
An 8'6" rod, reel with a drag, 8 wt rig with sinking tip line, for big water and saltwater.
A 9' rod, reel with a drag, 11 wt rig with sinking line, for the big saltwater fish.
Have plenty of leaders and inexpensive flies available. Learning to cast without snapping the fly off the end of the leader could take some time.