I can’t perform science experiments but retrieving space crafts

If you want the science from experiments, you must either transmit it, or return the experiments to the surface of Kerbin. The experimental equipment itself doesn't actually have to make it back to Kerbin though; A kerbonaut can retrieve the data and store it in a command pod that's headed back to Kerbin. There are some restrictions to this, though: you can't store multiple copies of the same experiment/biome/altitude combination, and I haven't seen a way of removing research data from a mobile lab. As a side note, you can store multiple crew reports by performing an EVA, taking the data from the command module, and then returning to the module.

Your experiments also don't have to be attached to the capsule when you return ‒ you can recover experiments returned as debris by disconnecting a science stage from a capsule; however this may be impractical due to limitations of the game where after a certain threshold, debris (or even whole aircraft/spacecraft) will be unloaded when in atmosphere, but it does mean that you don't need to perform an EVA to retrieve the data.

Some science experiments also have a transmission cap where as little as 25% of the data can be transmitted back to Kerbin; eventually, experiments must be returned to max out available science. However, when return is non-trivial, taking the hit in transmission might be worth it (for instance, if the target is the surface of Tylo or Eve). Take a look at the science wiki page for more information.

Don't go onto an EVA when you are still flying through the atmosphere or your kerbal will get blown away.

When you go on EVA, always press F as fast as possible to grab the ladder at the hatch. Sometimes the kerbal will already be on the ladder when you go on EVA and get right back in, but when he isn't, the chance is high that he will drift away when you don't grab the ladder quickly. When the kerbal goes drifting, you can activate his jetpack with the R key and attempt to maneuver him back to the hatch, but this takes a bit of practise.

By the way: You can also obtain science from the surface of Kerbin. It doesn't give you many science points, but every terrain type gives you other results which add up. It's enough to unlock the first few tech nodes. Low-hanging fruits to pick up early are crew reports, eva reports and surface samples from:

• Launch pad
• Spaceplane Runway
• Space Center (everything around the buildings which is not one of the two above)
• Shores (the flat plain around the space center)
• Grasslands (the slightly hilly area to the west)
• Highlands (the more hilly area further to the west)
• Ocean (your Kerbals can swim)

The first two can be easily picked up without even igniting your engine. The others only take a small sub-orbital flight (or a bit of walking)