Prepare a water bath canner, jars, rings and lids before beginning. The canner should be pre-heated to around 180 degrees F (barely simmering) for hot pack.

Juice the lemons and strain to remove any pulp and seeds.

Hull and puree the strawberries.

Mix the strawberries, strained lemon juice, and sugar in a saucepan.

Gently heat the mixture on the stove to around 190 degrees F, but do not boil.

Ladle the strawberry lemonade concentrate into prepared jars, leaving 1/2 inch headspace. Seal with 2 part canning lids.

Process the jars in a water bath canner for 15 minutes, adjusting to the altitude (see notes).

Turn off the heat and leave the jars in the canner for an additional 5 minutes to cool slightly before removing them with a canning jar lifter to cool completely on a towel on the counter.

Wait 12 to 24 hours, then check seals. Store any unsealed jars in the refrigerator for immediate use. Properly canned and sealed jars may be store in the pantry. Refrigerate after opening.

To reconstitute, mix 1 part concentrate with 3 parts water.  For a 1 pint jar, you'd add 3 pints water.  For simplicity, you can just add a pint to a half-gallon mason jar, which holds 4 pints, and then fill it up the rest of the way with cold water.

That should give you a "basic lemonade" flavor that's strong, but not too strong.  You can adjust to your own tastes.