Welcome from another newbie (to this forum at least). I have been running peps for about half a year, though, and have done a good deal of research.
First off, you will need bacteriostatic water to reconstitute your peptides. This can be had quite cheap if you go to the right place. I pay like 3.99 or something before shipping for real pharma bac water by Hospira. I've seen places charge as much as 9.99 for the same 30mL.
In order to know how much water to add, you have to know what concentration you want. Since a standard slin pin is 100 units/tics, one typically will set up the concentration so that your dose is 10 units (.1cc/.1mL). This makes things quick and easy for dosing.
For the GHRP's, there is a debate about how much to use. Some use as little as 100mcg (.1mg) per dose, some use 250-300mcg. I use 200mcg personally, and am about 190lbs at the moment. I don't have much experience with sermorelin, but IIRC that is dosed more similar to ipamorelin, which I dose at 100mcg.
To calculate your water, you will calculate compound volume/water volume (mcg/mL). If you were to add 1.5mL of bac water to 3000mcg of compound, this would result in a 2000mcg/mL concentration. When you pull a dose of 10 units on the slin pin, you will have 200mcg. This can be fine-tuned how you would like. For example, you can use 2mL of bac water in your 3000mcg to achieve a 150mcg dose at 10 units. For the sermorelin (usually more expensive than the GHRPs) you could use 3mL, giving you 100mcg per dose.
These peptides are very fragile chains of amino acids. To reconstitute, you must put your needle into the vial at about a 45-degree angle and push the plunger slow and steady so as to drip the water down the side of the vial without spraying the water directly into the compound. This is the same process used for hGH if you ever venture there. Once you've added the appropriate amount of water, carefully turn the vial on its side and spin it slowly like a cement truck to mix. Whatever you do, don't shake or otherwise subject it to shock.
I know you only asked for the reconstitution process, but please do ensure that you have your sterile process nailed down. Mine isn't perfect, but I use alcohol-based hand sanitizer after washing with soap and water. I then take 91% isopropanol (iso alcohol) and paper towel to wipe down the surface I'll use. After that, ensure to swab the stoppers of your vials of peptides and bac water with an alcohol wipe. Obviously don't touch anything else until you're done with the process. I store all the vials under refrigeration inside a glass container (plastic leaches/harbors bacteria) which I have wiped down with the 91% alcohol.
One other thing, stacking a growth hormone releasing hormone with your peptide is synergistic. I stack whichever peptide I'm using at the moment with Mod GRF 1-29 (aka CJC-1295 w/o DAC). Some use CJC-1295 w/DAC, but that provides a sustained GH increase instead of pulses like multiple doses of Mod GRF. Pulses are much more beneficial to the male than a sustained increase.
Anything else, just ask and I'll answer best I can. I know a little bit about peptides, even though I still have a lot to learn. Good luck and take'r easy, brother!