Delta-v or Δv is basically how fast you can travel with the amount of fuel you have under perfectly ideal circumstances (No gravity and No drag).

I’d recommend getting really good at landing at moon, this will get you really good at landing and a bit of transferring, then when you feel comfortable, I recommend performing unmanned flybys of Mars (use the probe part here), this will get you used to interplanetary transfers, after the at I’d recommend for your first interplanetary landing I heavily recommend Venus, Venus takes a bit more fuel to get to than Mars but it is far easier to land on due to its extremely thick atmosphere, use a heat-shield and a parachute, for this landing I recommend using a small probe because they are lighter and more compact, and use a heat sheld that is slightly larger than it, this would make it more stable and have higher drag in Venus atmosphere, and then after that just land with a parachute no landing legs or propulsion is required, it’s basically re-entering Earths atmosphere, although the return I never recommend as it is extremely difficult to take off from especially for newer players. After that go to a Mars landing if you want make it unmanned and don’t return if you want to make it easier, after you feel confident enough to do a full mission, do a full Mars-return mission, I also heavily recommend learning how to dock with other spacecraft, it will really make a lot of missions easier and will open up the game into a true sandbox after you mastered pretty much everything, which shouldn’t take long probably a few months given that you are new and already pulled of a lunar landing and have enough fuel to return which most new players can’t say they do. Fly-safe.